As a memory map and PDA user for my sat nav/GPS solution I have for three years been unable to use some of the main features on the hill as the battery runs out long before we get home, so I only use the system when navigation is tough poor visibility etc and stick to traditional map and compass for most situations (until I get lost). I leave the system on from the start of the walk until the end of the battery or walk whichever comes sooner for the data.
My real problem is, sadly I might add I like to analyse the data and store the track as a route for later, if the battery runs out on the fells I loose it all along with the navigation facility should the weather and my average traditional navigation skills turn pear shaped. I toyed briefly with the idea of buying a Satmap system until I realised that the hundreds of pounds I have spent on memory map maps would be wasted and I would have to buy them again as satmaps version.
Solution for less than fifty pounds I bought an extended life battery, (www.mugenpowerbatteries.com)for my particular PDA the battery life has gone from 4 hours to about 11 hours. The original battery 1250ma the new one 3000ma and it comes with a new battery door cover to accommodate the larger battery. It still fits in the otter box (www.otterbox.com) which keeps my unit totally water and bomb proof.
I hope this may be of some use to others if indeed there are any others with the same challenges