How I hacked my Garmin 310XT to last 37+ hours!

I am a runner with a preference for the really long runs. Kind of runs that last 20+ hours. So I have always been annoyed by the limited battery life of all GPS sport watches. The best battery life I have heard so far for a GPS watch is in the area of 20 hours. And I wouldn't like to be without it in the last stages of a race that goes on for 24 or 28 hours. But that is what is happening.

I have a Garmin 310XT GPS watch since 2009. This is a nice piece of equipment, that is quite reliable and providing about 18 hours of operation on a single charge. Unfortunately after these 18 hours I have to plug it using the bulky connector to a power source and it takes a couple of hours to recharge.

For my short runs I always go with my iPhone which is just fine for up to 5hours of activity recording. I like having a phone with me since I am a trail runner. So why bother carrying two devices. Bottom line is that in the last two years I have used the 310XT only a handful of times and this 300+ euros device was sitting at the back of a self almost forgotten.

I was racing a 100 miles trail running event in England last July and since it is fashionable there to run on unmarked courses, I was in desperate need for a GPS to assist me in my navigation for over 24 hours. One option was to use my eTrex Hcx with AA batteries that lasts for about 22 hours and change batteries somewhere in the middle of the race. But then I saw that 310XT on the self. I like hacking things. So I thought of opening the watch to see what kind of battery is using. Caution: This is an operation that has several risks especially for those who are not inclined to this kind of tech tricks.

The Garmin opens at the connection of the top metal grey and the mid rubber part of the case. I used a blade to open it with caution so that I would not scratch the case or damage the plastic parts. It was not such a big task and minutes after the watch was wide open. I removed the LCD screen (it is connected to the motherboard with a wide cable band) Then I removed the motherboard. The GPS sensor/antenna, is located at the lower part of the case, just under and between the two button labeled "reset" and "stop". This is a useful observation, since I need to know which part of the case must be facing up with no interference towards the sky in order to lock the satellites.

Just under the motherboard I saw the battery. It is a simple Li-ion 700mAh battery, that was not so difficult to locate at an online battery-store for just 23,49 euros. The battery is similar to the one of older Garmin Forunner 305 model. Keep in mind that it does not fit the dimensions of the 310XT in case someone gets the idea to replace the battery with a new one (because batteries are failing after 3 years usually). But it is the same battery according to the tech specs.

So I got the idea that I could add a second external battery to the 310XT, connected parallel to the internal one, so that I would double the battery life of the device! I ordered the battery from BatteryUpgrade.com and after a couple of weeks I had everything I needed to start the operation.

First I did a wooden mold a little bigger than the external battery and about as deep as the battery. I wanted to enclose the external battery in silicon so that it is not exposed to moisture and water. I sprayed a bit of oil in the mold so that the silicon does not stick to it. Then half-filled it with melted silicon from a silicon gun and while it was still liquid I placed the battery in it so that it was half covered by the liquid silicon. Once it cooled down the silicon was rigid, I removed it from the mold and repeated this procedure for the other side of the battery, so that in the end it was fully covered. Silicon did not leave any open gaps and sealed the battery completely.

I removed carefully the battery from the 310XT without disconnecting anything and exposed the poles that were covered with white tape. The red cable indicated the + pole. The same applies for the external battery I bought.

With my Dremel I drilled a small hole on the case of the 310XT at the bottom left corner and away from the GPS antenna. Remember, I do not want to put anything in front of the antenna. Through this hole I passed the two cables of the external battery (which I made a bit longer by soldering some extra cables).

I used a soldering gun to connect the two + poles together inside the case. I made sure that everything was ok by switching on the Garmin from the exposed motherboard buttons. It was ok. So I started assembling the watch again. I used some glue to secure the metal grey top cover to make it as safe from humidity as possible. The external battery was hanging out in its' silicon case.

I covered the silicon case of the external battery with some epoxy in order to make it more rigid and easier to glue on the 310XT case later on. It takes about 8 hours for the epoxy to dry completely.

I would like to notice that my Garmin 310XT has the optional Garmin fast mount allowing quick fix on the Garmin bracelet or on bike mounts. This is essential, since with the standard bracelet this operation will make it more difficult to have access to the recharging points at the back of the Garmin, but not impossible!

Once everything was assembled and dry, it was time to attach the external battery

on the Garmin case. I did that at the lower side of the watch, but away from the location of the GPS antenna that was inside. I did not want to block the signal.

I used epoxy glue again to secure the external battery and seal the small hole for the cables that are going inside the case. The watch is not waterproof anymore, but it can handle rain and sweat. I secured also the cables with some cable cover, for extra protection.

I tested the watch at recording mode a couple of times and it lasted for 37hours 30 minutes or more each time. It takes twice as long to recharge though. Also Garmin software is designed to measure VA so once the official 2.5VA are reached you get the message that it is charged, but it is not! The same applied when I am using the watch, after about 17 hours I start getting the message that battery is low because the 2.5VA are almost gone. But with the external battery there are more than 5VA available. So I just ignore these messages.

I used my modified Garmin 310XT during the Lakeland 105 miles event end of July. I uploaded the whole track and used the watch with the "Do track" feature. My race lasted 25hours 38 minutes. The 310XT worked throughout the race without any problems. I had to ignore the "low battery" warning from 17 hours and on. I also had to restart it at one point because the event was very long and the Garmin could not handle so many track points. But this was happening many times even before my hack. It restarted without any problem!

So, here I am with a unique GPS watch that lasts 37+ hours of non stop operation and it is only about 50 grams heavier than the normal 310XT. And I have it on my wrist all the time giving me a vibration everytime I go off track. This was the single most important piece of equipment for this race for me. It got me safely to the finish line after 105 miles on completely unmarked trails.

Lakeland 100 miler - 105 miles on trails at Lake District

These last 6 months have been quite different for me. The first half of the year included two major events for me: the Boston Marathon, and Lakeland 100 miles (105 actually). Besides these two events I had in my calendar some more secondary events: a 100km road run (Psatha, Greece, national championship for 100km) and one more 100 miler in England (the South Downsway 100miler).

Boston marathon and 100k national road championship were succesful. I crossed the finish line in Boston at 2:45:30 and given the difficulty of the course, I was happy with this achievement even though Ι did not improve my PB. Also at Psatha I won the 100k race in a decent time of 7hrs 52min.

End of May unfortunately, I managed to injure badly my ankle, and that kept me out of running till mid June (3 weeks off) and cancel South Downsway 100miler. This situation forced me to withdraw my participation at Spartathlon as well since the time was not enough (given all my other everyday obligations) to prepare for this, and I hate being stressed about something that I concider my hobby.

So with just 3 weeks of training I was getting ready to start the Lakeland 100 miler in the beautifull Lake District area in England. This is the most popular event of this distance in the UK and one of the most popular in Europe. Gathering more than 300 registrations (and more than 600 for the 50miler on same weekend). The race is an Ultra Trail event. The distance is 171kms and about 6.000m of accumulated ascent (as it has proven to be, despite the claim of 6.800m by the organizers). Most of it is on technical trails and the course is, following the English style, completely unmarked. During the 3 weeks after recovering from my injury, I managed to score some high miles, getting to about 120kms every week. But no long runs. My injured ankle needed time to recover. So with this background, I was getting in the airplane from Athens to London, 2 and half days before the event (Wednesday 24th of July). My friend and fellow runner, Nikos Petropoulos, was participating in this event as well, and the two of us formed the Greek team. We are the two winners of 2011 and 2012 editions of Rodopi Ultra Trail (www.rout.gr).

At the area of Manchester, we would be staying for Wednesday and Thursday, with our good friend and experienced ultra distance runner, Argyris Papathanasopoulos. Argyris and his wife, Hannisze provided exceptional hospitality! We run

together on some nice trails in the area of Lancaster (adding 9kms on Wednesday and almost 11kms on Thursday before the race) and  had some good food!!! On Friday morning, feeling relaxed and ready to hit the Lake District trails, we camped with our tent at the start area of the race which is at Coniston. It felt great being among all these happy runners, and I was happy to se that there was not even a hint of stress around us. Everyone seemed to be very calm and confident. Even my friend Adam Rose who was attempting his first 100miler ever (falling victim to some discussions we had last year...).

At 6pm everybody was lining up for the start. Almost 280 runners were ready to embark on this long round of the area. Me and Nikos were both relying completely on our GPSs for navigation. Our knowledge of the area was zero and obviously we have not done any of the recces on the course. Also following the road book was not an option for us, since our target pace for the race was not compatible with book reading! We wanted to finish in the region of 24 hours. Nikos had my Garmin eTrex Hcx and I had a Garmin 310XT that I have hacked to improve power duration (external battery providing about 37hrs of power time). They proved to be very good navigation tools for both of us. UTML has check points approx. every 2hrs for runners going at sub-27hrs pace. So we were both carrying minimal food and hydration. But the obligatory kit was enough to fill our backpacks. I have an objection to this kind of lists.

When I am on the mountains under foul weather and find myself in desperate situation I just want to have with me things needed to get me back to civilization as soon as possible, instead of spare clothes and stuff like this that will make me feel safe to stop and wait - which the worst thing to do under such circumstances.

The area has countless water streams suitable for refilling our water bottles. I used a Simple Hydration 320ml bottle that can be used as handheld, in pocket or at the back of my shorts bottle, and I think I will never run again without one! Best water bottle ever! The weather forecast was for clear skies and warm temps. At least until Saturday evening. That was an advantage for us, since running on the boggy and wet terrain that is typical of this race and area, would be really tricky! Even with no rain, for Greek standards, our feet were wet throughout the race. We started at our own comfortable pace, which placed both of us at around 30th place overall at the first two legs of the race. Many runners were going too fast! We gradually climbed up in ranking  during the first half of the race.

The night came and everything was fine for both of us. The route consists of mostly wide trails or forest roads, but there are some long stretches of technical trails as well, gaining altitude or loosing it quite fast. There are some steep uphills and downhills but, for our Greek standards, quite short in duration. The special attribute of the race (compared to other Ultra Trail races), besides the usually rainy weather, is that participants must be able to deliver fast running pace at the flat parts but also handle well the technical downhills. Most ultra trail races, have either difficult elevation profile and technical terrain, or require fast running pace. This event combines both, and that makes it quite hard. Trust me, running at 5:20/km on flat roads while130 kms in the race, is not something that goes soft on your legs at all!

Nikos and myself kept going, improving our ranking all the time. Half way, at the major station of Dalemain, we were already close to the top 10 runners, ranking 12th overall. And we were both feeling great! At Dalemain I had a problem, that would cost me at the later stages of the race. In my drop bag, I had a 670ml bottle with my mix of carbs, electrolytes and protein (4:1). Unfortunatelly, the mix was ruined by the heat and I realized this after we left the CP. I had to spill it and replace with plain water. This deprived me of about 500cals for the 2nd part of the race. I adapted accordingly my nutrition plan, adding more gels (which I do not fancy so much), and some electrolyte tablets that Nikos gave me. But my mix is essential to my nutrition and hydration plan as well as for my taste. I am always running based on liquid calories as much as possible. We kept going strong though. I was happy with the race, the landscapes are really breathtaking and I had no physical problem. Approaching Ambleside, which is about 30kms from the finish line I started feeling my energy levels low. I was still able to hit hard the downhills but at the short uphills I was feeling low and kind of sleepy. It was pay time for my 500 lost calories. At Ambleside we arrived at 14hrs 54mins at 10th place overall. I told Nikos to keep going and leave me behind to put some energy on. He did not want to. I stayed about 8-9 minutes in this CP which is a lot for me. When we started our way, within 300m I knew that I was not ok and convinced Nikos to split with me. I did not like the idea of delaying him any more and also making me uncomfortable trying to keep going. In this leg Nikos run 20 minutes faster than me. I kept going at a slow pace to give time to my body to short things out. At the next CP (13 out 14 in total) I have fallen back to 12th place and still feeling so and so. I stopped there for another 8-9 minutes. The crew there told me that the next runner was more than one hour behind me. I left the CP knowing that I had in front of me the last uphill and less than 15kms to the finish. So after  moving about 300m out from the station, I found a nice spot with some grass and layed down for a power nap. This was a bold decision so close to the finish line. But it proved to be a smart choice. 10 minutes after, I was feeling strong and healthy and starting running all the uphill. I caught Tom, the runner who was 11th at that time, before the next CP. We run together from that point on. Tom had GI problems but together we worked our way to the finish line.

I finished strong and healthy in 25hrs 38minutes, a bit more than 1 hour behind Nikos. Looking at my GPS files now I can tell that we have lost about 35 minutes in navigation Also if my nutrition/hydration plan was not derailed at Dalemain, I would have managed to stick with Nikos and hit hard the last legs. I believe that we could have done the UTLD in this 1st visit in less than 24hrs.

The event proved to be tough for the runners. Only 45% finished. Nikos was 10th and I was 11th together with Tom. I have the best of memories from this event. The volunteers in all CPs are amazing. The organization is exceptional. All the runners are very friendly and the landscapes are amazing. I would describe the terrain as alpine at low altitude. Many alpine-kind-of fields and trails, as well as rocky, but at altitudes lower than 800m. Of course if the weather was not so kind to us, things could be way more complicated. But weather makes each event unique every time we run it.

After the event my legs were just fine. I would dare say that at some of my hard

marathon races, my legs were more trashed than in this race. I think it has to do with the big patches of the route on soft grass and the absence of long downhills, even though there were quite a few steep ones.

Sunday morning we packed our tent, after a well deserved beer and night sleep on Saturday. Nikos and I started our long way to London by train and then to Athens by airplane.

We arrived 4am Monday morning in Athens. Monday was a working day for both of us.

Some details on hydration and equipment for this race: I had 18 gels in total I had about 600 calories in liquid form from my mix of maltodexrtrin, vitargo with electrolytes and whey protein (25% protein). My second serving got ruined. I drunk a few glasses of Coca Cola in some of the stations The only solid food I had was in the form of 2 sandwiches with cheese and 1 with peanut butter. Also had a couple slices of plain bread.

Shoes - Innov-8 Mudclaw. Backpack UltrAspire Kinetic Water bottles 1x UltrAspire 0,7l Human and 1x Simple Hydration 320ml bottle  Headlight Petzl MYO XP North Face t-shirt Adidas running shorts