XPR7550 dead Impres lithium battery and flashing red light

[g8tzl2004]

I attempted to charge an XPR7550 lithium battery which had not be charged for maybe 12 months and was completely flat (0.01v)

The standard Impress charger just gave a flashing red light. I left it for an hour or so as I assumed that the charger was "intelligent" and would attempt to "trickle charge" the battery from zero volts to whatever level the charger needed to start the fast charge routine. However the red light just kept on flashing. However there was some voltage being pulsed into the battery but the battery voltage did not appear to be increasing.

So I used a 12v 150mA trickle charger (from an old Yaesu FT290) to force a charge into the battery. I used the "inside" battery pads ( which connect to the actual radio) and had my meter in line so I could measure how the voltage was slowly increasing.

Under no load, the trickle charger measured 20v but when connected to the battery this fell to a couple of volts and started to increase very fast up to about 5 volts and then continued to slowly rise. At 5.5v I thought that this was enough voltage for the charger to recognise the battery and to start the charging routine. When I connected the battery I got a steady red light...but a few minutes later it was back to a flashing red light? So I reconnected the trickle charger and held it in place until the voltage was up to around 7.00v - this took about 15 minutes. When I again placed the battery in the Impres charger I now got a yellow conditioning light (which I did not want as I guess it starts to discharge the battery??). Anyway, I took the battery out and then put it back in (which is what you do if you don't want to go into the conditioning routine) and the red light came on and the battery now appears to be charging OK.

If I had left the 0v battery in the charger "flashing red" overnight, would the battery have eventually charged up or did I have no option but to force a trickle charge into the battery?

The charger is still on red so lets hope its now fast charging OK!!

[g8tzl2004]

UPDATE: The impres battery fast charged OK!!

I have now tried another dead Impres lithium battery.

I used the same trickle charger. I had the following effect with the 1st battery as well as the 2nd battery.....I was trickle charging the battery and the voltage had risen from 3v to 6.8v...but when I disconnected the trickle charger, the battery voltage dropped to 0.5v...it appeared that voltage was going in and the voltage across the battery was slowly rising but the battery was not charging?? Anyway, I tried "pulsing" the trickle charge...by just removing the trickle charge for a second every 5 seconds...after a couple of minutes the voltage dropped to 6.3v and then carried on slow climbing. I measured the battery voltage again and it was up to over 6v with no charger connected. I left the battery trickle charging until it hit 6.5v and then put it in the Impres charger.

Now the red light is constant and the battery is fast charging in the Impres charger.

I'm wondering why the battery appeared to be trickle charging but was not but then (after a bit of pulsing) suddenly started to retain a charge and was good to go for the Impres charger once I hit 6.5v?

I'm also still wondering if I had left the Impress charger flashing red overnight whether the dead battery would have recovered without forcing a trickle charge?

[N4KVE]

Whenever I have a problem like this, I shock the battery by connecting it to a 12 volt 20 amp power supply for 5 seconds. Then installing it in the proper charger for a regular charge. Brings them back to life. GARY

[RFguy]

What version of firmware is in the charger? I recall there were enhancements made to the firmware for dead battery recovery at some point.

[g8tzl2004]

Charger model and firmware version - WPLN4226A v3.9

I have previously zapped Nicads and NiMH's but I always thought that you had to be careful with lithium batteries as they are liable to explode!!! Hence I used a "safe" trickle charge!!

I wonder how many "good" XPR batteries have ended up in the trash?