I'm doing some last minute faffing and as I do near every trip, worry about out how much battery capacity I need for HT550, primarily to ensure my eTrex 32x GPS has juice, but also to top up my phone (usually left in flight mode). Despite using them for a good year now, I'm still unsure or rather have little confidence in just how long I get out of a set of rechargeable batteries in the eTrex. Sometimes it seems ~24 hours, other times considerably less.

How do you lot work this kinda stuff out? I think it's the not knowing if or when I'll get the chance to plug in and recharge from the mains that's getting to me more than it usually does.

My thinking out loud: The rechargeable batteries I've got hold 2333 mAh so 4666mAh/pair. Realistically, I think this means I'll get <2 charges/pair from a 10000mAh powerbank, so starting with 2 pairs fully charged I'd hope to get 4 days riding at best done before running flat. Ergo 2 x 10000mAh powerbank ought to see me good. Or 1 x 10000mAh and 1 x 20000mAh so I've some spare for my Phone.

BUT even a 10000mAh capacity powerbank takes about as much space as 6 or even 8 AA batteries, so putting any environmental concerns aside, perhaps I'm better using single use lithium AAs to give maximum battery life and just perhaps carry a couple of rechargeable AAs as back up.

Knock 10% off any source capacity for a transfer or if you prefer add 10% to the capacity of what you are charging.

I dug out my kit breakdown for the HT5500 - https://bobwightman.blogspot.com/2017/0 ... l-kit.html there's also a post on dynamos which looks at power consumption - https://bobwightman.blogspot.com/search ... namo%20hub.

I used a Garmin Oregon so a bit bigger screen than the Etrex but I had pretty much all the power saving setting dialed that I knew about. A fully charged set of batteries will do a day's riding unless you are at the pointy end and riding through several nights. So you need enough charge for four or five more days depending on your intended pace. Of course you can get AAs just about anywhere. There are large sections of the route where you don't really need to navigate so you can turn off the screen - somewhere like the track of a thousand puddles, once you start it you are riding it for a couple of hours with no junctions to confuse you; Tollie Path to Kinlochewe - it's just a road so ride it! etc. I had mine on a 30sec timer after which if I wasn't scrolling on it it would turn off.

If I were to do it now I'd take two 10,000mAh batteries - if one failed then I'd still have another.

Lithium AA's in the Dakota, phone on max battery saver mode and switched off when not needed. I carry a 'charger' which takes 4AA's just in case the GPS dies and I need to use the phone for nav or I need to make a long phone call.

Idiot proof!

Thanks Both: I'm really just overthinking things as I'm prone to do. Once I'm riding then things'll be reet, but I'll faff while I can.

You’ll be fine with a few lithium AA’s . I used to use a Garmin GPS66 with AA’s in expedition mode, used to get three days. Now using a Gamin530 in powersave mode which just flicks into life when you are approaching a turn or head off course and get a couple of days easily and then boost from a 20,0000 Anker power bank. Not sure what the etrex power settings will be but I guess as long as you have a spare set of batteries there are enough places in the North you can get re supplied if needed

Mr G wrote: ↑Mon May 19, 2025 9:48 pm You’ll be fine with a few lithium AA’s.

To be honest, I never used to fret so much when I used single-use lithiums as, as you rightly point out, they last an age. It's since moving to rechargeable that I've paid more attention. Anyway, I realised I'm being a daft b'stard and just taking an extra pair of AAs will suffice. Panic over.

I went with 2x 10,000 powerbanks.
Also consider how fast they charge - some are pretty quick these days

For what it's worth, bearing in mind my info is a good few years old but Garmin did not recommend the use of rechargeable batteries in the early eTrex range.

I think when fully charged a rechargeable cell delivers 1.2v under load whereas a non rechargeable Duracell or similar will start off at 1.5v.

Also, the capacity of a good rechargeable is about 2500mAh but a non rechargeable Duracell is 2850mAh or up to 3000mAh if you are rich and can afford lithium-ion.

Itchynuts wrote: ↑Wed May 21, 2025 2:47 pm For what it's worth, bearing in mind my info is a good few years old but Garmin did not recommend the use of rechargeable batteries in the early eTrex range.

I think when fully charged a rechargeable cell delivers 1.2v under load whereas a non rechargeable Duracell or similar will start off at 1.5v.

Also, the capacity of a good rechargeable is about 2500mAh but a non rechargeable Duracell is 2850mAh or up to 3000mAh if you are rich and can afford lithium-ion.

This is where something like these is useful. My wildlife camera will burn through a set of normal rechargeable batteries in a night but these last ages.

https://amzn.eu/d/iixjRPv

Itchynuts wrote: ↑Wed May 21, 2025 2:47 pm For what it's worth, bearing in mind my info is a good few years old but Garmin did not recommend the use of rechargeable batteries in the early eTrex range

The 32x is ok with them and you can pick which battery type you’re using in the settings so it knows. Single use lithium are by far the best longevity-wise, but I feel I should be using multi-use ones. I know, I know, in the grand scheme of things and all that but whatevs …

johnnystorm wrote: ↑Wed May 21, 2025 4:11 pm This is where something like these is useful.

I have something similar. The capacity isn’t as good as the ones that use a regular charger but they’re well convenient.