I use 12V 3700mAH NiMH “Vapex” race pack from www.component-shop.co.uk . They are terminated in a Futabs connector. I splice in an extra lead so it can connect to charger (or 20W solar panel) and rig simultaneously. I connect a Futaba connector to the FT817 power lead so I can just plug it in. I also have a Futaba connector on a fly lead connected to my PSU so it’s a simple case of just plugging in there if I want (save mucking around with the pole terminals that have a load of other gubbings connected to them.
These packs aren’t as cheap as an SLA at about £20, but they are half the weight for same capacity and can be charged far far quicker. The shape is “longer and slimmer” than the SLAs and is far easier to slip into the pocket in clothing or backpack or whatever. Mine fits neatly in my small Explorer hard case, along with rig, tuner, balun, mic, cables, Palm Mini Paddle and so on. Can’t do that with an SLA! They can also be recharged when not completely drained with no loss of capacity. Empty to full is in an hour or less using a nice variable current charger also from Component Shop. The charger uses a temperature sensor to detect full charge of the battery.
Pete M3KXZ G-QRP 11767