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Beginner with battery tech here, so forgive my naivety :)

I'm making a portable bluetooth speaker, and am wondering about the best battery solution to use.

The amp needs 60W max, and accepts 12-24V. I would like the charging circuitry to be contained inside the speaker so that I can simply connect a laptop PSU (19V) to a jack in the back to charge it. Ideally would like a runtime of at least 2 hours @ 15W.

At the moment I'm between Li-Ion and Lead-Acid (open to others!)

Essentially - which is the easiest/cheapest to install charging circuitry within the unit for? (I don't mind building a circuit but I'd rather not if possible :) )

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  • \$\begingroup\$ How long do you want it to run for? \$\endgroup\$ – Brian Drummond Nov 10 '16 at 18:15
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    \$\begingroup\$ Do you care about being relatively lightweight? Or compact? If so, definitely go with lithium (ion or polymer) vs lead acid. It is a big difference. Also, most lead acid batteries are 6 or 12V. Neither of which will work well for you since you need 12-24. If you choose the right number of cells (say 4 cells in series) you can probably use a lithium pack without any type of regulator. Just a low-voltage cutout at 12V. You would need to design in charging circuitry. \$\endgroup\$ – mkeith Nov 10 '16 at 18:26
  • \$\begingroup\$ Lightweight is important, yes, but if it's cheaper and easier to go with SLA for the sake of an extra 500g I don't mind. You make a good point about the nominal voltage of the Lead-Acids. \$\endgroup\$ – Ben Nov 10 '16 at 18:39
  • \$\begingroup\$ You could probably just put 4 high quality protected 18650 cells in series and not worry about balancing. If you make sure they are balanced to start with. \$\endgroup\$ – mkeith Nov 11 '16 at 5:46
  • \$\begingroup\$ So 4 brand new 18650s with a protection board will do it? Something like this ? \$\endgroup\$ – Ben Nov 11 '16 at 9:22
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Li-Ion have a significant advantage over Lead-Acid batteries for power-to-weight ratio. You may also be able to get better efficiency out of your (undisclosed voltage) laptop PSU with some series connection of Li-Ion cells closer to the charging voltage.

With the rising popularity of Li-Ion cells available, there are also a wide variety of charging modules which you can build into your gadget. They will provide proper charging as well as discharge protection.

Ref: https://en.wikipedia.org/wiki/Power-to-weight_ratio#.28Closed_cell.29_batteries

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  • \$\begingroup\$ Thanks for your reply. I have had trouble finding a charging/balancing module that deals with Li-Ion cells in series - I can only seem to find "protection" modules, which prevent over discharge etc. \$\endgroup\$ – Ben Nov 10 '16 at 18:36

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