I have a Yaesu VX-2R hand held and it is a great rig. I wanted an external battery with more capacity. The maximum voltage for an external battery is seven volts and there are no seven volt batteries. An economical, initial purchase price, approach would be to use a 6 volt gel cell battery which is actually 6.3 volts.

However, I have a bunch of AA NiMH batteries and I decided to build a battery pack from them. A gel cell battery would be more cost effective, but it weighs more. Five AA batteries at 1.4 volts each result in a total of seven volts when fully charged.

The problem was finding a suitable container. I have a large supply of peanut butter jar lids. They are very handy on the work bench for holding little parts that would otherwise end up on the floor. Five AA batteries fit very nicely in a larger lid with not much wasted space. I used two lids to hold 10 batteries and the result is a 4,600 mAh external battery. Just glue the lids together and drill a small hole for the connecting wires. You can easily make the battery pack water proof.

I taped the batteries together and soldered them with small solder wicking braid. The braid is much easier to use than solid wire and it certainly can't be faulted for current carrying ability. Be sure to tin the ends of the batteries before soldering the braid. You will damage the batteries when you solder them. No matter how good you are there will be a damaging temperature rise in the batteries. The excessive temperature will reduce the number of charge / discharge cycles you will get from the batteries.

Commercial battery packs have batteries that are spot welded. The spot welding temperature is much higher than soldering but the amount of time to spot weld is just a fraction of a second so the heat that is transferred is much less.

I further molest my batteries by charging them at a constant seven volts from a simple variable voltage power supply that I built with a LM317 regulator. The batteries get warm and if I am keeping an eye, hand, on them, I disconnect them from the power supply when the get warm. I try not to charge them for more than 24 hours at a time.

NiMH batteries are supposed to be charged with an intelligent battery charger that does all sorts of nice things while recharging the batteries. So how bad is life when you are as slovenly as I am? NiMH batteries are advertised to have a life of 1,000 charge / discharge cycles. Let's say that the soldering reduces that by half and brute force recharging reduces that by half again. The result is maybe 250 cycles. My guess is that my battery pack will last me several years and by that time it will be obsolete anyhow.