Another upgrade
Why?
So far Magayon II has consumed 3 AGM batteries since December 2014. That is roughly one battery every three years. Which is at the lower end, the literature states lifetimes of 3-5 years. Maybe because of the high temperatures in the tropics? Or deep discharge? But they were always connected to 4 solar panels, so deep discharge should not have happened. Before buying the fourth AGM battery it makes sense to look at alternatives. One is to switch to LiFePo4 technology. The advantages are:
- Higher energy density, meaning less weight and smaller size at the same capacity compared to lead acid or AGM batteries.
- Build in battery management systems (BMS) that besides regulating the charging and preventing overcharging also prevents deep discharge.
- Longer life, most manufacturers specify 2,000 charge cycles for LiFePo4 batteries, some up to 4,000.
- No danger of fire or spilling of battery acid.
- While they still cost more than led based batteries, given the longer life time they are cheaper in the long run.
Magayon II already has two LiFePo4 batteries with 48V and 50Ah each for running the electric outboard motor. So after a bit of research on prices I decided to build another LiFePo4 battery for the 12 V system.
Battery Cells
Using recent data on cost and charge cycles of AGM and LiFePo4 batteries with different capacities I calculated the cost per Ah per charge for the different types. With around 0.23-0.24 Pesos per ampere hour per charge, AGM batteries are around 4 times as expensive in the long run compared to LiFePo4 batteries (0.045-0.095 Pesos per ampere hour per charge).
I decided to go for 120 Ah, around three times the current capacity. Since Magayon will be used a lot for short trips, and is going back to the Marina with grid connection afterwards, it is a different scenario then before where the power supply relied totally on the solar panels. Having higher capacity will also allow running a small cooler with Peltier elements or topping up the motor batteries a little bit.
This went totally wrong. I ordered four battery cells online from a supplier in the Philippines. He sent used cells. I returned them immediately. As of August 4, 2024 I am still waiting for the refund. It’s more fun in the Philippines.
I also asked an expat who is installing solar systems and has provided the equipment for the catamaran of a friend. But he did not even bother replying, maybe he is only interested in selling complete systems.
BMS
After a lot of reluctance I decided to order a smart ANT BMS directly from the company in China through Alibaba. It arrived two weeks later with FedEx and looks all right. Probably that is the way to go. Identify the manufacturing company’s presence on Alibaba and order from there, rather than through dubious local distributors. But finding the official outlets of companies in Alibaba is quite difficult.
So as of August 4, 2024 the construction of the new battery is on hold, until I can find some reliable source for cells. It is not highest priority anyway.