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Alternatives to using a D type battery


New Member
I have a machine that throws a tennis ball for my labrador and it works fine. The only issue I have is that it uses 6 x D type batteries and these sell for about $20 a set and last for 24 hours.

As you can imagine, the cost will mount pretty quickly if used every day. From what I can gather online, they are 1.5v each and produce up to 20,000mah. It can be plugged into the mains electricity but this makes it non-portable and also means using a long extension cable.

Can anybody suggest an alternative way of powering this machine with batteries? ie. something that will last longer and be rechargable or is the best setup these D type batteries.



Well-Known Member
Most Helpful Member
If it's arranged as six cells in series (so nominally 9V), two lithium cells in series should work equally well.

eg. Using some holders for 18650 type cells, either two in series or four arranged as two series pairs connected in parallel, depending on how long it must last on one set of batteries.

Then a set or two of good quality 18650 cells and a separate charger.

The individual capacity is rather smaller than the D cells; realistically those could be 10AH, while genuinely rated 18650 cells are likely somewhere around 2.5AH

I'd guess it's averaging half an amp while running, but the peak could be much, much higher.
Or does it's power adapter have any data, if that is a separate unit?

Using loose lithium cells in parallel means you must be very careful to only fit ones that have an identical charge state.

If is needs a higher capacity battery system, it ideally needs packs making up with permanent interconnections between the cells, so they always have matched charge levels; eg. packs with four pairs of cells in parallel to give 10AH.

That is turn means the battery must have a "balance" system or be charged with a separate balance charger.

Another possible option is a something like an 18V (or 20V, same things) power tool battery plus a switched mode voltage regulator to take it down to around 8V.
That means ready built batteries and chargers. You can buy battery adaptors for various types to use them with different things, on eg. Amazon or ebay, or some there are some designs on sites like Thingiverse, if you have access to a 3D printer.

But you must know how much current the machine uses, to find a suitable voltage converter.


New Member
wow... thanks for all the tips.

I've been in contact with the manufacturer but they didn't have the amp draw stats available to hand. The D cell Li-Ion battery might be the easiest option, even at £66 for 6 of them, it may work out a lot cheaper in the long run,.

Thanks again.


Well-Known Member
Most Helpful Member
You could also use D type NiMh rechargeable types, which may be cheaper.

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