I want to make a battery pack with mains charger to power my tablet that has a wonky battery. It lasts all day if I do not use WiFi, but with WiFi it dies within the hour.

I have 4 Nokia BL-5C 3.7 V 1000 mAh and 2 Nokia BL-6C 5v 1000 mAh batteries (but no way of charging them.

Is there a way of using either of the batteries I have (in series?) and make a circuit to charge them while still connected to the tablet via its DC in?

I was told at Uni by a techie, that I need to make a charging unit, but has a "step down" out put to the DC in of the tablet. In theory it could charge and supply power at the same time, but with a switching circuit would act as a plain battery?

  • \$\begingroup\$ I'm handy with a soldering iron, so a simple schematic / diagram is OK ;) \$\endgroup\$ – John Nov 25 '12 at 23:24
  • \$\begingroup\$ got a battery spec and tablet P/N? \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Nov 26 '12 at 4:42
  • \$\begingroup\$ Hi Richman, All I know is.. The 4x BL-5C 3.7v 1000mAh. Pinouts are + O – Type lithium-ion, 3.7V Capacity:1000mAh/1200mAH Max Charge Voltage:4.2V The 2x Nokia BL-6C 5v 1000 mAh. Pinouts are + - O Type lithium-ion, 3.7V Capacity:1000mAh/1200mAH Max Charge Voltage:4.2V The Tablet is a MID-2910 and takes 5v 1000 – 1500mAh Cheers John \$\endgroup\$ – John Nov 26 '12 at 15:53
  • \$\begingroup\$ Have I asked the impossible? Or is this project feasible? \$\endgroup\$ – John Nov 28 '12 at 10:00
  • \$\begingroup\$ it might be more feasible to find a laptop battery/charger pair on surplus then add a 5V converter output with a 5 day capacity. Or simply buy a replacement. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Nov 28 '12 at 15:01

It seems you want to charge cellphone batteries in parallel. This is not a safe thing to do. You would not get much energy out from it either.

If you want to build an external battery I would suggest building it from 18650 cells. You do always need to be careful when working withing lithium batteries, so if you thing that you might not know what you are doing, then don't do it and buy a ready-made battery pack instead.

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