Rough estimate of the life of the battery can ship the claimed amount of charge / discharge cycles. Please note that many manufacturers are cunning, indicating the number of cycles, when tested in standard conditions, and it is overpriced. Another common problem of poor-quality batteries – it's too fast to self-discharge. Reasons may be several. For example, savings in the production of lead plates of lead-acid batteries, or savings in production process, as it has significance not only the mass of the lead plates, but their shape and location. Thin cheap housing can easily crack with acid leakage, and in addition, contributes to the rapid self-discharge due to poor insulation.