good way to keep spare batteries topped off??

[JBotAlan]

Originally Posted by Bill_B

This is one of those things for which you have a hard time remembering the source. I'm pretty sure it is mentioned in a presentation given by Al Sk. for the 2009 conference session. 2009CON_Robot_Electrical_Design_Skierkiewicz

Wow...thank you!

http://media.wpi.edu/News/Events/Rob...ierkiewicz.wmv

That is a wonderful presentation! I would definitely recommend it.

[Al Skierkiewicz]

Since someone has posted about using the clips to attach to the Anderson plugs, I feel I need to address that for two reasons. The first is that it is impossible not to scratch the surface of the contact using this method. The scratches reduce the effective contact area to a fraction of what is needed. The result is a high resistance contact that is prone to heating. The heat can reach a point where the connector will actually melt and burns are also possible.
The second, is not as obvious. The clips are now connected to a battery that is capable of producing currents high enough to weld. If they were to short together not only would this current flow but a high risk of battery damage or fire could result. Do not use the clips connected to the Anderson plug contacts to charge batteries.
If I see this at an event, I will remind you. The Anderson plug with contacts is listed for $3.50 on the AndyMark site. Pretty cheap insurance considering.

[ErikRantapaa]

Thanks for all of the discussion on this topic.

Questions:
- Is it OK to charge the batteries in parallel? (I realize it will take longer.)

- Are there any safety issues with placing a depleted battery in parallel with fully charged ones?

[Alan Anderson]

Originally Posted by ErikRantapaa

Is it OK to charge the batteries in parallel? (I realize it will take longer.)

Don't do it.

If you have taken great care to ensure that two batteries are in exactly the same condition, always being charged and discharged together for their entire lifetime, you can get away with it. If not...don't do it.

Are there any safety issues with placing a depleted battery in parallel with fully charged ones?

Yes, there's a big safety issue. The depleted battery will pull current out of the charged ones. Depending on how depleted it is, it can suck a lot of current. Things will get hot. Insulation will melt. Smoke will appear. Fire will burn. Demons will roam the...well, you get the picture.

[Al Skierkiewicz]

To piggy back on Alan's post above think Ghostbuster's real wrath of God stuff. OK not that bad, but don't do it. There is no good reason and a lot of bad ones.