40 V lithium battery, voltages across the 4 connectors?

[Stephen Tashiro]

The 40 v lithium batteries for several brands of electric lawn mowers have 4 connectors on them instead of two. What voltages should I expect to measure across these connectors when the batteries are fully charged? (For example, are there two "hot" connectors and two grounds? - or one hot connector and 3 grounds? or are there two pairs of connections for two 20 V cells?) The chargers for such batteries also have 4 connectors, so I have the same question for them.

My particular case is "Greenworks" 40 V lithium ion batteries, models 29462 and 29472.

[Dan Hintz]

Lithium battery chemistry typically requires a smart charger... extra pins are going to be for temp sensors, voltage balancing, communications, etc. Looks at a laptop battery... 8-pins or more, quite often...

[Jason Roehl]

A couple of those connectors are more than likely used for internal protection circuitry--they'll shut off the battery if it's too hot or cold, or if it's fully charged or discharged (over-charging leads to a runaway chemical reaction and fire, discharging too far will kill the battery). That said, 40V is almost certainly a nominal voltage, and fully charged, it should read around 45V or more somewhere, but you may not be able to make that reading from outside the battery pack due to the circuitry.