Presumably once the APU is running and or ground power is on, then the batteries are no longer needed, except in an emergency, and could be isolated.
So why not treat them as primary cells and do a swap-out before flight and have the charging system disconnected? The batteries could then be recharged under controlled conditions on the ground and inspected before being used.
That is of course presuming the problem is only due to charging.
I'm probably missing something as it seems too simple a solution, albeit a temporary one.
Can you imagine the logistics nightmare that would cause.
Servicable batteries required at ALL line stations. Maintenance time to change the battery. These a/c get turned around in less than 90 mins. Disconnecting the power for 30 mins while you change the batteries would kill that. How many function checks would be required after the swap to ensure the system will work as required.
Then there is the problem of transporting hundreds of batteries all over the globe.
Alternatively you have charging workshops on every line station.
I can't see the airlines wanting to carry the cost of any of that.
Multiple APU starts?....cobblers! it has to cool for 30 minutes otherwise the Turbine-shaft apparently distorts(bends)S0, fire it up and the first thing it does is recharge it's own battery....well. that's what sound practice says it SHOULD do,,,,but the demonstrated masters of fudge and kludge may have a different view.
That 30 min cool down period is a temporary arrangement. A work around. It was certainly not the intention from the manufacturer. It became apparent during service. A permenant fix to the rotor bow will appear in good time.
I take the point though. A Nicad battery would suffice. It has for other types so why not this? Commonality of parts is the only reason I can think of.
Oh, and saving weight.
