If your STIHL 36V battery fails to charge, but you know the voltage is lower then the charger will accept, you might be able to revive it. Here are two popular methods for getting the charger to “see” your pack once more:
To boost it with a second battery, you will need another battery. It can be any other 36-40V battery or even another STIHL pack. I’ve had luck using my 40V Greenworks battery since its voltage range isn’t far off from the 36V packs of STIHL.
Before you do anything, locate positive and negative terminals on both batteries. This is important; getting the wrong polarity will destroy both batteries in an instant. Double-check labels before touching anything.
Looking closely we can see the Stihl AP 300 clearly labeled. It’s rated at 36V with 6.2Ah of capacity. Other labels on the back show who made it and what certifications it has. Now you’d have to flip it over to check underside terminals to know which one is positive and which is negative.
Once you do that, it’s time to prep your donor battery for hookup. The terminals on the Greenworks pack are pretty much the same so it’s easy to match up. Before plugging in, though, you want to check voltage with a multimeter first. On this test setup I used a KAIWEETS display. That read 36.26V.
So connect red wire to positive and black to negative. That way you know everything is hooked up right from the start. Checking this twice helps avoid accidental short circuiting when boosting.
Remember to connect positive to positive and negative to negative. Once you have your leads in place, use both units to maintain stability. Be careful not to touch any shorting points with your hands while holding the wires.
Only let it connect for about 15 seconds. Don’t let them stay connected too long as they might overheat. If there is any sign that something is going wrong, disconnect immediately.
If your wires are touching the terminals just lightly, so much the better. The red wire should touch positive contact point exactly, and black one should touch negative side securely. This step takes a little time, but be sure to go slow and not rush because bad contact or even sparking can happen.
Once you have boosted for 15 seconds or so, unplug all cables and recheck the charger. Sometimes this takes several tries. Reconnect to the charger again just in case. When the slow blink green light appears, the charge is underway. It may seem slight, but it’s the real thing!
Method two using a DC power supply
Alternatively (and this one’s direct), use a DC power supply rather than an additional battery. Bench top units provides accurate voltage settings. Start with a setting between 30 and 40 volts out. Don’t exceed 1 ampere because it prevents overloading weak cells during recovery. Limiting current to 1 ampere is safe because it prevents overloading weak cells during recovery.
Because batteries naturaly charge gradually, using a supply like this that ramps up voltage over time is closer to reality than boosting from another battery.
“Now it starts out showing just 30.00 volts on the screen and there’s zero amps being drawn because you haven’t got any load attached yet. Watts are still zero until then too. You want to set your charge accordingly to the suggested specs only. Your current should be kept down so you don’t damage internal components.
As intended voltage creeps upward gradually. Everything is monitored carefully so that everything stays in check and doesn’t go off the rails because things are accurate with these lithium chemistries. I insert red wire down into terminal section below while it’s still reading thirty volts on the power supply. There’s no current moving around the circuit obviousy yet.
Wait till you have solid contact before pushing anything higher. Keep your hands away from live parts completely. Always put safety first in every procedure.
As the voltage continues to rise gradually it reaches 36.12 volts, and the screen will reflect this readout in real-time. Because this connection was so brief, no amperes is showing either. Just as previously described, you keep it short for only as long as necessary. There are no problems yet and no signs of trouble either. There’s no smoke, no melting, thank goodness. Disconnecting quickly keeps any hidden dangers away.
Lastly, the battery gets returned to its place inside the orange AL 300 charger bay. Instead of flashing red, the green LED simply stays lit. Additionally, several charge bars light up on the front panel as well.
After everything was done, it looks like your dead battery has indeed been revived. Then, the battery starts charging again normally. You used some simple troubleshooting methods and resolved the issue all by yourself. You should of checked the voltage more carefully before starting. It would of been safer too.
