I bought the Bluetti 150 (1500 Wh) a little over a year ago and recently after discussing the math with a roommate who’s a physics major, I realized the math against the draw down on the indicator vs the watts being pulled does not add up (it’s been this way since I bought it).
Here’s what I am normally running:
1 set of LED lights (barely registers - always reads “0”)
1 diesel heater (the chinese ones - I think you know what I’m talking about) which when starting, will pull between 45-95 W for about 5 min, then settles into 3–11 W continuously.
1 laptop which is a Macbook pro mini that is currently charging at 47 W and my meter on the laptop says it will be fully charged in 2 hours.
My understanding of fthe math is as follows:
1500 wh = 15 hours of juice (give or take) with 100 W discharging continuously. With 5 bars on the meter, that roughly equate to 3 hours of 100W per bar.
On a typical day, I’ll have 4-5 bars when I wake up. When I start my heater and run it for MAYBE 30 min to warm up the van, I lose a bar - happens every time. We’ve had pretty good sun so throughout the day the solar will bring that back up again so I never really worried about it, but that doesn’t seem right.
In addition, when I went to bed last night, I had 2 bars. I’m on a quick trip and thought I would test how long it took 2 bars to disappear. I had nothing plugged in to draw anything down, and when I woke up this morning, it had dropped to 1 bar.
So what’s up? Can I trust the display? Is the display malfunctioning?
The bar column battery gauge is an approximation and not an actual meter with exact % remaining. Fore example…if there is one bar showing, that can mean anywhere from 20% to 39%. If you are very close to the 20% range, it takes very little usage to drop off the one bar of capacity.
Secondly…when the unit is on and no loads are connected, you are still drawing power from the EB150 being on and additional power will be consumed by the inverter and regulated DC outputs being on as well. If you are fully charged and turn the EB150 completely off you will not have any power drain over weeks. If you keep the EB150 (or other model) on in the standby mode it is perfectly normal for the battery to drain even though you do not have any visible exterior loads connected.
Think of the battery gauge the same way the fuel gauges worked in cars in the past. The miles it took to move the gauge each 1/4 tank was not linear and was also not an exact display of the remaining gallons in the tank, but rather a representation of the approximate amount of fuel left.
My limited experience with this on the EB150 (and I assume the EB240, since they are essentially identical other than size, weight and battery capacity) is that this is a “guessometer”. (I love my EB150, but I don’t like the display at all, and I wish more would go to a percentage display.) When I charged up my battery to full and then drained it using a 500W space heater (so about a C/3 discharge rate), it definitely took different amounts of time to see one bar disappear. It took little time to go from 3 bars (out of 5) to 2, but it stayed on 2 bars for what seemed like twice as long.
One thing I would add is, don’t expect 1500 Wh of usable output. That is true of any so-called “solar generator”; a good inverter might get 85-90% of that. Some of the capacity is held in reserve to prolong battery life, and the operation of the unit requires some power itself.
The EB150/250 has a certain power draw when it is on even if there is no load. Typically, the AC inverter will draw 1% of its max rating even when there is no load. So a draw of 10-15w even when nothing is plugged in is normal. It is too bad that the power meter doesn’t show this drain, my old goal zero shows that, when the 500w inverter is on, it draws 4-5W.
In addition, a 1500wh battery will not provide 1500wh of power when discharging through the inverter. Due to reserve capacity, idle drain and inverter inefficiency, you can expect around 80%-85% for a large current draw C/3, less for smaller draw. So the 1500wh battery would likely only power a 100w load for 11-12 hours or so.