Cycling UK Forum

On tour, is it worth carrying a GPS?

My old eTrex is good for about 8 - 10 hours continuously on a full set of new NiMH's, if you're lucky (and that's with the energy saving options selected.) The ads say 17 hours - which I've never experienced.

With older batteries it's more like 4 - 6 hours. If it were a longish wild camping trip with no recharge option then GPS would be a waste of space - unless you fancy carrying 100 sets of charged NiMH's (which slowly discharge, anyway).

Are those 2500 mAhr NiMh cells?

I would say yes it is.

I poo-pooed the things (understatement) for years but eventually got an Etrex 20.

It's very good though it has taken me about 18 months to fully understand it and the various route generation tools of it and software/online tools.

Batteries last about 24 hours I think - so 3 days of 8 hours.

Techies will tell you that you shouldn't use one-hour chargers (bad for the batteries apparently) but good on a tour - fairly easy to find powerpoints every few days.

Are those 2500 mAhr NiMh cells?

Energizer recharge 2450 mAh. These are new ones and the packet says, they'll hold a charge for six months. They certainly wouldn't hold a FULL charge for anything like that, so the claim is moot.

Batteries last about 24 hours I think - so 3 days of 8 hours.

Have you tested that duration in actual battle? If true, I'm impressed. As mentioned, my battery life with GPS has always been less than brilliant.

Techies will tell you that you shouldn't use one-hour chargers (bad for the batteries apparently)

Quite true. I picked up a rapid charger a few years ago as I was fed up with day long recharges. They charge quickly at the expense of cooking the batteries. They get damn hot and could even be a fire hazard. An electronics bloke I know, told me to throw it away.

The 17 hour duration is I believe for non rechargeable cells. There is a huge difference in battery quality, and no set standard for rating capacity. A 2000 mah battery may give 1900 mah at a 0.2 amp draw but only 1500 mah at a 0.5 amp draw.

With years of aero modelling experience, my choice has currently (sic) come down to Vapextech Instants http://www.vapextech.co.uk/ which are an excellent spec for a GPS application. Other makes such as Sanyo are equally as good. I would always recommend using a smart charger.

mm, maxglide - been using my Maplins one-hour charger and batteries for 18 months or so and all seems well - appreciate that it is very probably not the best thing for the batteries but surely it can't be as bad as you say. In the meantime I would have used a fortune in normal batteries. And fire hazard? - surely there would be a basic legal issue here which would have come to light? Do you have any evidence/stories? Since it's so fast I am never of course out when it's on. On the bike I'm afraid it will have to be a one-hour charger set-up anyway. My bog-standard mobile (you'd be horrified if you saw it) charges fairly fast and I aint dumping that - anyway I have 2 spare batteries for it.

Thanks for that link hexhome - I value your opinion - could you point me at the particular batteries and charger from their range which you use?

all the best folks

Portland wrote:Thanks for that link hexhome - I value your opinion - could you point me at the particular batteries and charger from their range which you use?

I've found these to be excellent batteries http://www.component-shop.co.uk/html/in2500aa.html which are ideal for low current draw applications such as GPS, radio RX and TX etc. They would not be my first choice for high current applications such as cameras.

As for chargers, I personally use an expensive specialised model from Schulze but this would be ideal for these types of battery http://www.component-shop.co.uk/html/tg2900.html , in fact, I've just bought one!

One of the advantages of a smart charger is that it senses each cell individually rather than treating them as one battery and potentially overcharging one or more cells.

@Portland
The only evidence is my batteries & charger became uncomfortably hot, hence I returned to the old trickle charge brick. I've used Maplins cells and their large 20x packs are good value.

hexhome, thanks for the link.

Thanks for the info hexhome.

I think my Maplin charger is maybe semi-smart on your definition - you can use a discharge cycle pre-charging if you like (I do) and I have noticed that it seems to sense batteries individually - even in a pair taken as used from the GPS it will often show some discharged before others and so start to charge them while others are still discharging.

Also when it gets to charging all 4 AAs it shows some finished/fully charged (I think maybe it then goes on to trickle charge) before others.

Yes maxglide I think my batteries get hot/warmish when charging but I think they cool once it reckons they are charged.

I stress that I accept that longer charging is better.

Sanyo Eneloop batteries. Awesome!

I had about 19 hours and 190 miles out of a pair of Uniross 2100mah Hybrios last weekend.
I would expect around 24 hours from Sanyo Eneloop XXXs at that rate.

If getting around 8 hours I would suspect that one of the cells has failed probably from allowing the unit to go completely flat which makes one battery wreck the other.

While touring, I have 4AA batteries for a four day "cycle" 2 in the GPS and 2 in the rear light.
They swap over after 2 days, the GPS leaves enough in the batteries for whatever riding after dark is needed.

There are also 4AA batteries in the big front light that will come home 3/4 full almost every time to cover any possible shortfall.

To extend that to 8 days I could

Carry 4 more batteries 110g
Buy 4 disposable batteries (against my principles).
Risk using the headlight batteries as in summer, wild camping, I dont use it much.

In real life I do contact civilisation, so I could carry a Uniross Globetrotter charger (110g) and fast charge my batteries four at a time whenever I access a power point.

If going totally wild, I can install the dynamohub and recharge the AA batteries four at a time inside my headlight, I have never resorted to this measure, except to check it works. (500g extra weight)

Back to your GPS.

Possible current drains are compass left on or backlight left on.

Are you actually running it flat or going on the bars in the display? As it is old it may not have been updated to read NiMH batteries, the GPS can be updated to do this through your computer. It will not extend the life that you get out of the batteries but will make the bars in the battery display go down more slowly.

I still think the problem is most likely a seriously unbalanced pair of batteries, a battery charger with individual cell charging and display soon weeds out duff cells and they are not that uncommon, even new.

@meic
I haven't used my eTrex on a bike. The info is from day long hikes (in the desert) of about 50km. The heat may be a factor, although most are in the cooler months. I switch the thing on, wait a few minutes for signal lock, and I'm off. It stays on for the duration. Good for 10 hours, but I haven't tried the new cells yet. It's an old unit too - the old yellow eTrex. My newer Vista lasts a bit longer. Newer units probably have more efficient power profiles.

The old B&W Etrexs were noticeably worse on battery life (and not just because the batteries were worse back then).
Warm gets much more out of batteries, I have had temperature related flat batteries even in May in the UK due to cold (below around 6 centigrade). This is what led me to using the low self discharge batteries, they do not suffer as badly when the temperature drops.