Welcome to the SOTA Reflector!
Further to replies above and in a similar vein. An 8.2Ah you would not in theory be allowed on an aircraft which might be why supply is difficult. I ordered a 10Ah about 8 years ago from China and I’m still waiting for it to arrive. Far better to use smaller batteries and harness them together. I have two pairs of 5Ah which I used last weekend. I used to have a 13.2Ah which was actually three 4.4’s in parallel. These big batteries were and sometimes still are used for a 100W radio.
All these have worked well and I have had no trouble apart from the usual swelling which seems to eventually occur with most of them paralleled or not. I un-parallel them for charging normally but I’ve had no problem charging while paralleled on many occasions using just one of the sense/ balancing connectors without trouble. NOT RECOMMENDED however.
You will get more flexibility with smaller batteries and the choice of stacking them or using singly for lighter applications
73, John
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Another thread which may be of use to you?