Don't.
Reputable battery manufacturers have shown tremendous difficulty in getting these damn things right and stable, but above all, they've shown that you can hold them responsible.
By all means buy a cheap battery if you have good fire coverage.
Even apart from the fire part, which I'm not *really* exaggerating, cheap batteries are prone to premature failure, so you end up buying two of them in the same time.
Our techs are staying the hell away from them, and that's always a clear sign to me.