Battery Type for the Power Box

Lead Acid Battery

Out in the field the electrical supply of my telescope is based on a lead-gel battery so far. This design is proven. It is robust and quite harmless as well – if one thinks on the horror stories told about the accidents with this tiny little Li-Ion „bombs“. Anyway I see two disadvantages which are closely related to the lead-acid design:

  • The battery is heavy. My big block with a nominal capacity of about 500 Wh weighs about 17.5 kg.
  • The nominal capcity is not really available. Even though my battery is specified as deep-cycle it is not advisable to draw signtificantly more than 50% of its nominal capacity without decreasing life time.

Li-Ion Battery

In contrast the Li-Ion based power supply realises significant higher capacities at lower weights. Reasons for this are the higher energy density of the Li-Ion technology and the fact, that the nominal capacitiy is more ore less fully available.

The disadvantage: In case of a short cut or mechanical injury a thermal runnaway could damage the system and hence endanger people!  For similar reasons a battery management system (BMS) is mandatory in order to assure correct electrical handling during charging and discharging.

Due to the ebike boom the Li-Ions in the 18650 size are large spreaded in the market and – at least in my opinion – have a good technical readiness level.

Possible Alternative

LiFePo4 batteries could be probably a better energy source for a telescope. The offer an energy density which is comparable to the Li-Ions, but don’t suffer the thermal runnaway risk  as Li-Ions do. At the moment (summer 2019) the price is still to high for my impression. The Li-Ions in the 18650 size are under a pretty good price pressure arising from the ebike market.