can i buy re-chargeable Lithium AAA batteries with charger for my garmin geko from anywhere ?
GPS'S dont half go through them dont they!

www.7dayshop.com

go for the ones with the biggest mah
rating.

Unfortunately the answer to your question is no you can't but there is a great deal of confusion around this issue. Fristly there are to types of lithium batteries currently on the market lithium and lithium ion. The crutial is that lithium are just high power sigal use batteries Theses do come in AA) where as lithium ion are rechargeable such as the ones in modern mobile phones. Lithium ion batteries aren't produced in AA size because the recuire a special charging circuit unlike NiCd on NiMh and so would explode in an ordinary charger. and it is belived that the public are to stupid to read the instructions and charge accordingly.
Your best be as above is to go for a high mah rated NiMh set

Look up Vapextech rechargeable batteries on eBay. 2700mah ones are very good, 8 for £7.95.
I use them all the time.

I don't think you can, unless the technology has changed since I last looked. I think rechargable lithium cells are 3v - se here:

Lithium rechargable

Most people use nimh. I would agree with Ghastly and get the highest mAh. I would disagree about 7dayshop though. I bought some from there and two were dud when recieved and the others not much cop.

I know there are a few battery experts in this forum.... can anyone explain this? I use a single NiMH AA for my Navman R300 GPS trip thingy. Uniross 2000mAh work fine, even Aldi FiF 2100mAh work, but some fancy Powermart 2400mAh jobbies will not work at all.... but are fine in other applications.

Make sure you fully de-charge them before re-charging too as this gives them a full charge instead of a top up!!

from personal experience don't buy cheap batteries, they not cheap in the end. i've had too many duds. i use ansmann photo aa and aaa. high rating, extremely reliable in performance and charging so far.
any well respected brand will do i think e.g. sanyo

i picked a lot of energiser nimh cheaply (4 have now died out of 12), they're fine for non-critical stuff. they have let me down too many times outdoors.

that said, i'm sure there are some extremely good cheap battereis out there. it may just cost you lots trying to find them.

Most rechargeable batteries lose their charge quite quickly, but these Hybrio ones hold it much longer. I have found them ideal for my gps.

Apart from the lower self discharge of the Uniross Hybrio batteries (0.1%/day against 1%/day for normal NiMh), they also have better low temperature performance. They don't seem to publish this fact, but I have had it confirmed by Uniross. They seem to use the same technology as the Sanyo Eneloop which does have a published spec at 0 deg C.

Another factor in maintaining rechargable batteries in good condition is to use a good quality charger. The best ones will charge each cell individually (rather than in pairs).

There seem to be some new NiMh batteries that are supposed to keep their charge for ages (I think the main Vapextech seller oneBay has them). They sound interesting - I frequently keep a spare set of normal NiMhs for by GPS but they do lose their charge and need topping up.

The Uniross Hybrio batteries are rated at at least -10 degrees C , see http://www.batterylogic.co.uk/hybrio.htm