If those headline usage figures are correct (I would question how the data was arrived at), it's no wonder London fire brigade reports so many bike fires. Where I live it'd be a struggle to see 2,800 journeys a year. (Perhaps a slight exageration) So, as mentioned earlier, it's a matter of percentages and degree of abuse. There are NO delivery riders around here, oh and no fires reported. I wonder if the two could be connected?
As to charging. I have 3 batteries in the collection.
!. An Ezee rack battery (around 14Ah) re-celled by Jimmy (r.i.p.) a few years back. It has always had a high quality fan cooled 4A charger. The connector is what I would call an XLR plug. The 3pin type you get on microphone cables.
2. A soft pack (14Ah) built by Jimmy. 2A charger with XLR plug.
When charging I use the fan output to blow over the 2A charger to help cool it 'cos it gets hot.
3. A rack battery on the wife's Big Bear (14Ah ish) also recelled by Jimmy a few years ago. This has a very slow charger rated at 2A which also gets hot and has the barrel type plug. I suspect it's lower than 2A though because it's the slowest of the lot.
Chargers get hot, batteries don't, not that I've ever found anyway.
If I were to advocate for a type of charger plug it would be the XLR type. Both plug and socket are robust construction and can only be put in one way round. There are different pin configurations that could be used for different voltages so they couldn't be mis-connected. If moulded on plugs were used then it would become obvious if some numpty had changed the plug and charged with the wrong voltage.