Batteries and design rules
IO-540
Many aircraft, particularly gas-turbine heliciopers and small turbo-props, have Ni-Cad batteries charged directly from the constant voltage bus - Bell 206 JetRanger amongst others. They do have overtemp warning fitted.
The new generation Ni-MH batteries currently under development have a patented charging system to allow use in environments such as aircraft, and the designer is confident we'll have them in certified aircraft in the not to distant future, and certainly in gliders in the UK very shortly. They are already in service with the UK and foreign military forces for specific roles (not yet primary aircraft power as far as I'm aware)
Rod 1.
I mentioned CS23.561 with my Part 21J hat on - in EASA land, I'm required to show compliance in design with the latest standard (21A.101) unless I can show good reason for staying with an older cert basis. I accept that many LAA type aircraft don't come under this rule, but if I was to certify a design in an Annex 2 aircraft (Tigermoth etc) under my BCAR design approval, I'd still have to meet the same design criteria, as the BCAR approval is piggy-backed on the EASA Part 21J approval and has to use the same design rules and procedures.