here's someone's response to a similar question i posted a while back -

floyd

Check the cables and connections at the battery and the starter; the big cables, both power and ground. Ensure the starter is tight to the block. The issue may not be a "small" battery but a resistive connection. If the starter circuit requires excessive current to turn the engine over, there is not enough energy left to charge the coil. You can check this by monitoring the battery voltage at the posts. A large voltage drop while starting is an indication that the starter circuit is pulling excessive current. Cold weather will aggravate this condition just as it would a weak battery.

As for the mechanic's suggestion that the battery is too small; check the rating on the battery. If it is at least 450 Cold Cranking Amps, you should be good to go.