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What Batteries Do I Need

by Brona Werritt
(York)


I have a 3000w (constant) 6000w (intermediate) invertor currently running off two truck batteries with split charger. This is running a dual fuel coffee machine, grinder and pump with total requirement of 925watts on an intermediate basis. I want to change the batteries and also fit a pie warmer and fridge with a constant 900 watt requirement for appreox 6 hours. Is this possible with current invertor and what batteries would I need. I can't use a generator as this is a mobile unit visiting numerous sites daily.

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by: MobCater

Great question! Since you're running a mobile catering setup without a generator, you'll need a battery system that can handle your power requirements efficiently. Let’s break it down step by step and see if this helps.

Understanding Your Power Needs
Current Power Consumption:
Coffee setup (intermittent): 925W
Pie warmer + fridge (constant): 900W
Total intermittent load: 925W
Total constant load: 900W
Total peak demand: Around 1,825W (when everything is running at once)
Duration required: 6 hours
Battery Capacity Calculation
To determine the battery size, we use the formula:

Watt-hours (Wh)
=
Power (W)
×
Time (hours)
Watt-hours (Wh)=Power (W)×Time (hours)
900W (constant) x 6 hours = 5,400Wh
Intermittent load (925W) depends on usage, but let’s assume it runs for 2 hours total:
925W x 2 hours = 1,850Wh
Total energy required:
5,400Wh + 1,850Wh = 7,250Wh (7.25kWh)
Battery Type & Sizing
You need a battery bank that can provide at least 7,250Wh of energy. However, since lead-acid batteries should only be discharged to 50% to extend lifespan, and lithium (LiFePO4) batteries can be discharged to around 80-90%, you’ll need different capacities depending on the type.

Lead-Acid (AGM or Gel) Battery Option:
7,250Wh ÷ 50% usable capacity = 14,500Wh required
Since 12V batteries are common, we convert:
14,500Wh ÷ 12V = 1,208Ah total battery capacity needed
This would require 10-12 heavy-duty 12V 120Ah AGM batteries, which is a very heavy and bulky option.
Lithium (LiFePO4) Battery Option (Recommended)
7,250Wh ÷ 90% usable capacity = 8,050Wh required
Using 12V lithium batteries:
8,050Wh ÷ 12V = 670Ah total
Best setup: Four 12V 200Ah lithium batteries (or equivalent).

Can Your 3,000W Inverter Handle This?

Your inverter is 3,000W continuous / 6,000W peak, which should be sufficient since your highest possible draw at any one time is around 1,825W.
Verdict: So there may not be a need to upgrade the inverter.

Final Recommendations

-Best Battery Choice: 4x 12V 200Ah LiFePO4 batteries
- Inverter: Your current 3,000W inverter is fine.
-Charging: A DC-DC charger from your vehicle alternator + solar panels (if possible) to keep the batteries topped up. You should also provide this info to a battery supplier who will provide a more accurate case study

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