fortunatly it does not get that cold here. Plus I dont have a block heater.When my batteries crapped out I swear I could spin it by hand faster than the starter but it always started. Kept it warm with the block heater and made sure the fuel system was good and tight till I got some new batteries.
ya well with the help from people here I have fixed bad connections,have the proper glow plugs and timing as close as possible.If the IP/injectors/glow plug system is in really good shape, it'll fire within a couple of revs and you don't need much battery.
If not, well... you need a /lot/ more battery.
I've started IDI's with one battery before; if the battery is in good shape(or it's warm), it's fine. If it needs much cranking... well, that's why you have two.