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I'm attempting to use a BPL3650 36v Ryobi battery as the power source for replica electric willy's jeeps I've constructed for my kids.

  1. The batteries charge fine in the standard chargers available off the shelf
  2. The batteries work fine in the standard Ryobi 36v tools and respond as normal to the pressing of the battery stength indicator

However, when I go to use them in a circuit not in a Ryobi tool, they only appear to show 18.6v across the positive and negative terminals. I can exclude them from the circuit and just test the batteries with my multimeter and get 18.6v. Bizarrely, the actual behaviour the batteries exhibit is to start off at around 39v and over a period of about 10 seconds, drop to 18.6v (or approximately half voltage) as indicated by the multimeter. However, the batteries are actually fully charged.

There are 4 terminals on the battery, the middle 2 appear to be thermistors (designated T1 and T2)and when I opened the charger to have a look, only one of them was connected to the charging circuit board.

I'm 'assuming' that the battery must be getting some form of voltage across the second thermistor when in the actual hand tools that disables the battery protection circuits. Apart from dismantling a Ryobi 36v tool to see what might be triggering the circuit protection in the battery, I thought I'd post here to see if anyone has any thoughts or had already achieved this process themselves.

In short, does anyone know how to get the full 36v+ from a Ryobi battery outside a Ryobi powertool?

1/4 scale jeep partially finished

Update: Ended up dismantling a 36V strimmer to see what was going on. In the first picture below you've see the trigger switch (Jaiben DBW-2036E). The multimeter before the switch exhibits the same behaviour as before but after the swtich, a steady 41v. Would someone be able to tell me what the electrical component is that's connecting the two poles after the switch? All I can read on it is 10A so assuming amps of some form.

Switch Details

Mystery Component

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  • \$\begingroup\$ Chanches are that the socalled BMS (Battery Management System) is preventing the use of the battery outside the tool the battery has been designed for. If you can open the battery and take a look. Maybe the circuit inside is simple. Probably not. Open the battery only if you know what you are doing. Lithium batteries can explode and catch fire if not handled properly. \$\endgroup\$ – Decapod Oct 30 '16 at 13:31
  • \$\begingroup\$ That jeep looks fantastic! Great job. Sorry I can't help with the electrical question. \$\endgroup\$ – mkeith Oct 30 '16 at 18:59
  • \$\begingroup\$ "The multimeter before the switch exhibits the same behaviour as before but after the swtich, a steady 41v" - makes no sense. How can the voltage after the switch be over twice as high as before it? I suspect your meter is lying. The component is a diode - and the switch does not boost the battery voltage, it only reduces it. "I'm 'assuming' that the battery must be getting some form of voltage across the second thermistor when in the actual hand tools" - is the T1 or T2 terminal connected to anything inside the tool? \$\endgroup\$ – Bruce Abbott Nov 20 '16 at 0:21
  • \$\begingroup\$ Hi Bruce, I wrote poorly above. The Battery Management System appears to cause the 39-41v at battery terminals to quickly drop away to ~18v as the behaviour constantly exhibited. Hence trying to identify the component. 100% agree that the switch would only cause loss so at this point I'm in time, I'm 'assuming' that the diode across the poles is dealing with the battery management. I'd be surprised if the momentary switch was causing it. There is no connection at all in the tool to T1 and T2, which I found surprising. T1 is connected in the charging base unit. \$\endgroup\$ – sturmstrike Nov 20 '16 at 4:00

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