Does anyone know how to read the code on a battery.
There is normally an alpha numberic code either hot stamped into the top edge of the battery, or on a sticker attached to the battery, or in many cases both. Various companies use slightly different versions and may have more info in that stamp than just the month and year, but all that I'm familiar with use a letter for the month (A=January, etc., skip the 'I' so that M=December)and a single digit for the year (0 through 9). The letter may come first, or the digit, depending on the manufacturer.
As an example, you may find a stamp like this:
9M 321XL That would be a December of 09 build date.
When purchasing a wet cell battery, try to find one that is no more than two or three months old. Batteries self discharge even when just sitting on the shelf in a box, and if allowed to sit for any significant length of time in a discharged state, that battery will permanently lose some capacity. It's a good idea to carry a voltmeter with you when making a purchase, and check the open circuit voltage. A fully charged battery should be 12.8 volts minimum across the terminals. Always fully charge a new battery before installing it in a vehicle.
Jerry