I plugged in my Hart 40V battery and the status panel on charger said what was going on. Normally I get a steady green light charging or a solid light charging when the battery is full. This time it was an irregular red light blinking instead.
It turns out the charger picked up an error on the battery pack and refused to charge it.
Some Hart 40V batteries were on hand for this. One was the bad battery which kept giving the red error light and the other was a good battery which charged fine. They were both 8Ah batteries with HLBP06 model number on the label (basically identical).
Bad battery never charged, it just flashed the irregular red pattern every time it was put on the charger.
Fixing Hart 40V Battery Red Error Light by Temporarily Paralleling With a Good Battery
Checked first if the bad battery still had charge left in it. One blue LED lit up on the gauge when I pressed the battery indicator button on the side of the pack. So there was some power there that ruled out a dead cell.
There was still some charge in the battery but no charger worked.
Each Hart battery has model number, specs and warning icons on the bottom. It also says where to find the positive and negative terminals. Metal contacts sticking out from the bottom of the battery pack are terminals.
I knew which terminal was positive and which was negative before I did battery connections.
I checked charge levels after putting batteries back on the work mat. Pressing the good battery lit up several blue LED bars showing much higher charge level. The bad battery still showed 1 bar.
This was logical to me.
I just fix it by temporarily putting the two batteries in a short wire with ring terminals on each end. The red wire is usually positive and the black is negative. Good battery gives power to bad battery and it starts working again.
By doing that I bypass the charger so the bad battery gets charged from the good one.
I wired the positive terminal of bad battery to positive terminal of good battery with red wire. Ring terminals on the wires are over metal contacts on the bottom of battery packs. Then I ran black wire from the bad battery negative terminal to the good battery negative terminal.
Now both batteries were in parallel.
The batteries had to stay hooked up about 15 seconds after the wires were connected. Some charge can move from the good battery to the bad battery without overheating the wires. It is a warning, wrongly connecting the wires or shorting the terminals will make the wire melt or smoke immediately.
When that happens, the connection has to go broken immediately.
I watched the connection for the full 15 seconds to see if it had heating or smoke. Wires were cool and no smell or trouble was apparent. When time was up I just pulled the ring terminals off both batteries with pliers.
Nothing unusual happened on the connection itself.
So I gave that apparently bad battery another shot at the Hart 40V charger that rejected it earlier. Battery label showed same warning text and model number as before. The battery itself was not different.
Placed the bad battery back on charger & checked LED status panel. The charger gave a blinking green light this time instead of the irregular blinking red error light. Battery is charging normally as shown by green blinking pattern.
That fix worked great.
The charger kept blinking green as the battery charged. The charger status panel has labels for different light patterns: power, testing, error, charging, and charging complete. I saw the green light still blinking.
The battery came back to life after doing the parallel connection trick. It was accepted by the charger and the battery started charging as the good one had done originally.
