Hello Martin,

MG> If you don't mind the physical size, use a 7Ah 2v SLA (SLA = Sealed Lead
MG> Accumulator, Aka A motorcycle BATTERY) with a continuously attached
MG> float-type charger and a solid state 12v->3v DC converter.

Why not make it +5.1 Vdc= in stead of 3 V?
Note the Pi is very critic at 5 V, so make that 5.1 Vdc= !
Even a low voltage drop would reset the Pi.
And make it at least 3 Amps for the new Pi 4B.

MG> This will definitely work and looks like it can be assembled for around
MG> 40 quid.

I have seen it at the RISC OS.be and T.I.N.A. Linux club in Mortsel.be
near Antwerp.

> OTOH the GP Batteries GPACCMP10002 M-Series Portable PowerBank, 10,000mAh
> Teal for 30 quid and you'll need a 5v wall-wart to charge it plus input
> cable (another 10 quid, so $40 in total). The Rapid Electronics write-up
> says that this unit has "Pass-through charging - recharge your devices
> and the power bank at the same time" which seems like what you need.

> The price estimates given above are all from the Rapid Electronics
> catalogue, so it looks as if there's not much price difference between
> using a Lithium-based power or an SLA-based solution.

Some people want to sit at the best chair there is
for the most lowest price possible, normally paid for a bad chair.

Henri.

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