good seller for rechargable pp9's batteries?

[geoff]

OK - what was the 27v square section battery a bit larger than an AA battery called?

And what was it used for

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[Scott M]

That would be a flash bulb battery. Remember a rather wonderful flash gun my grandfather had that had one of these in. It had a parabolic reflector in about 8 segments that unfolded by rotating around the bulb socket.

[Scott M]

Although, thinking about it, they were 22.5v. I've a feeling the 27 might have been a model number.

[Andy Dingley]

PP9s are pretty rare these days. The only ones I have left (four) are two old radios and a pair in an LCR test bridge ('70s op-amp technology needing two rail supplies)

For the radios I used two six AA plastic battery boxes and some recycled press studs. The battery life is probably much less than originally, but who cares, it's still long and rechargeable batteries are cheap.

The LCR test bridge is used very rarely, so I just plug some PP3s in there on home made adapters. Lasts for the hour or so I've ever needed to use it for in one sitting.

For NiMH in general, either the pairs from the pound shop (throwaways for kid's toys) or else Recyco from CPC seem to have good shelf life and the best service life in terms of cycles. Aldi & Lidl do great chargers, but their cell brands fail in no time.

[The Natural Philosopher]

WE called em 'hearing aid batteries'

hearing aid probably in the days of teensy valves.. Used em in valve model radio control. 27.5 v ...actuall;y

[Andy Dingley]

By starting with really old ones, with thick zinc cases.

They're easy to recharge - just shove some Coulombs in there. There are two problems, first you would otherwise break the electrolyte, so you have to do this with biased AC instead of DC - about twice the current going one way than the other. Use a resistor and diode in parallel (maybe another resistor too, if your supply isn't already current controlled). Secondly you'll etch pinholes in the zinc case. This is why an old thick-case one (probably a cardboard outer) allows a few cycles, enough to demonstrate the principle to the kids. A modern one (if it's both modern and still zinc carbon) is probably the very cheapest and nastiest cell possible, so it will break if you stare hard at it.

[Theo Markettos]

Since the OP wants PP3, how about:

self discharge PP3, so should hold charge while in the drawer (assuming the OP ever does switch off the unit before putting it away :)

That was the first hit on Google - there are probably other manufacturers/vendors.

Theo

[The Natural Philosopher]

If you can cope with a special charger and making your won pack a couole of lithium cells make a pp3 sized pack with a start voltage of 7.4 and an end voltage of around 6 if you are prepared to be clever about NOT running them flat.