Lithium Batteries Buyer's Guide—Part 3, Current (Amps) ...

Creating an offshore lithium battery system can be tricky, but rest assured, we're making progress. In the previous sections, we discussed the importance of understanding our power requirements and how to select compatible components.

We will get to a simple checklist of buying criteria soon. Tackling a couple more in-depth topics will ensure that each checklist item is backed by a solid explanation. We need authentic understanding, not just:

1. Watching YouTube videos.
2. Installing a subpar system.
3. Realizing later that it could have been much better.

The best news yet is that doing it right won't necessarily be more expensive. The cost-effectiveness hinges mostly on whether you choose a DIY route or opt for a larger battery bank. A detailed cost analysis will be provided soon.

Understanding Peak Current (Amps)

Now, let’s delve into the amount of peak current (amps) our system needs to supply. No, this isn't commonly discussed on YouTube, but it's crucial.

One must consider:

Many boat lithium battery systems deliver less peak current than quality lead-acid batteries.

It all comes down to the Battery Management System (BMS) and how robust the internal wiring is. More on the BMS below.

Deep cycle battery capacity is usually indicated by amp-hours (Ah), measured often at 20 and 100-hour rates. This represents the energy a battery can deliver under different discharge rates. For instance, a battery rated at 100 Ah can supply 1 amp for 100 hours before being considered fully discharged. However, the total amp-hours decrease as the current draw increases.

Lead-acid batteries have no-load resting voltages ranging from 11.8V (fully discharged) to 12.7V (fully charged). Inverters typically operate within the voltage range of 12.0V to 14.5V; falling below the minimum voltage triggers low voltage protection, shutting the inverter down. When powering a 1200W load, multiple batteries configured in parallel are necessary to prevent the voltage from dropping below the inverter's operating range. Repeated cycling below 50% capacity significantly shortens the battery's lifespan.

For true deep cycle use, you might need high-quality batteries that are not commonly found at wholesale retailers. A bank of four Group 29 batteries rated at 110 Ah each, wired in parallel for a total of 440 Ah, could deliver 220 Ah at 50% cycle with a no-load voltage of 12.2 volts. A significant current draw will cause voltage to sag below this level, triggering low voltage shutdown in the inverter. Thus, a 1200W load might run for 1-1.5 hours on these four batteries before triggering protection.

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