I've had the new Turnigy batteries out on the bike twice now, and both times they've performed as I'd hoped. So I've just put in an order for eight more, which I'll make up in pairs to give four 5Ah, 29.6 volt battery packs. I've also ordered another charger, because one charger can only charge up to eight batteries, using the parallel adaptor I've just soldered up.
When you do parallel charging, the batteries that you're charging need to be at about the same voltage. If one is part-used at 3.9 volts, and another is fully used at 3.2 volts, as soon as you connect them in parallel for charging, huge currents will flow from the more charged to the less charged battery, and that's not good for the batteries.
So, I anticipate ending the day with a bunch of fully discharged batteries, and a pair of partially discharged ones. And that's why I need at least two chargers.
After I placed the order, I went down to the workshop and soldered up the eight-way parallel charger, and the adapters that I'm using so that the batteries each present a kettle plug as their main input/output. Doing that, finally used up the roll of solder that I inherited from my father, 60 years ago. This is Savbit multicore solder, and it's always worked well for me. Thanks, dad.
I have another tube of Savbit solder ready to go, and a spare on order.