I drained my chassis battery by leaving our propane refrigerator operating, because I do not yet have a 30 amp plug at our house for shore power and I did not want to operate my propane generator to keep our green chile frozen until we left NM this coming Sunday. I have removed the battery and have put it on a trickle charger and I was curious about when it was built. On another website, I found that the date of origin is stamped on the negative battery post. In our case it has the numbers 21 and 12. That means it was built in the 21st week of 2012. After I reinstall it, I will find out if I could have charged it using the propane generator which has its own battery. That is, if the battery will charge.