Lithiums can hold a charge for a long time but usually limited ampere output for short time. Chief
??????
Li batteries, depending upon the chemistry, can handle loads upwards of 10C or ten times their capacity in discharge current. Impulse current can be upwards of 30-70X capacity.... A lead acid battery would implode if asked for anywhere near 10C for anything more than a few seconds........
I have physically started a Yanmar 3GM with a 6Ah Li battery (Race Cell brand). This is a 28C average load with the in-rush starter load approaching 65C. No 6Ah lead acid battery on the plantet, that I know of, will start a 3GM....
Also keep in mind that Li batteries such as LiFePO4 are Ah rated at 1C. So a 400Ah LFP bank is rated for 400Ah's at with a 400A constant load!!!
A 400Ah lead acid bank is rated at a 20 hour discharge rate for Ah capacity. This means that at just 20A & 80F it will deliver 400Ah's. Apply more than 20A and you won't get 400Ah....
That said....
These little jump packs are
entertaining for the size and the price they have come down to, but...
I bought a Noco GB-30 but it failed to start 3 boats so I returned it. I then bought the Noco GB-40 it too failed to start boats with dead batteries. I have since tried others and they all failed and some failed DANGEROUSLY by physically de-soldering themselves....
With the Noco's "capacity" of the battery is simply too small to jump large marine batteries at low states of charge. I unscrewed and opened up the Noco GB-40, which claims 1000A (peak), and inside I found a 2150mAh battery which equates to just 2.15 Ah. This is considerably smaller than the battery that powers my freaking iPad which is 7,340 mAh or 7.340 Ah. I have gone back to using my AGM based jump pack, which is 22Ah... If these little lithium jump packs can get upwards of 20Ah, with larger cables, I may jump back in but my Noco was nowhere near that and as far as I am concerned is nothing more than a misleading scam with completely bogus specs.
BTW the soldering inside the Noco is horrific and the relay that passes all the current is rated at 70A.... 1000A?? A friend who is also an electrician bought a no-name Chinese jump pack and on the first use the cables got so hot that it unsoldered itself. I bought a different Chinese one and SAME THING..
Also be very wary of how the mAh rating (1000mAh is 1 Ah) is derived. For example is it a 30C, 10C, 2C discharge or a 0.2C discharge to earn that mAh rating? These batteries are often asked to supply a 30C plus load and on diesels often in excess of 40C... Even a massive 12,000 mAh jump pack battery (12Ah my Noco GB-40 was 2.15 Ah's) delivering 400A is a 33C load or 33X its Ah capacity..
What is the Peukert of these jump packs at 33 X Ah capacity? My Noco claimed a peak amperage of 1000A (400A cranking). At 400A (through a 70A relay) that is a 186C load or 186 X the 2.15 Ah capacity of my Noco GB-40. What is the Peukert of that 2.15Ah battery at 186C????? Anyone who tells you lithium has no Peukert is simply full of bovine dung..
Most of these packs rely on your battery
not being completely dead. They will actually start a motor without the batteries in place easier so be wary of those shady & misleading videos. The reason for this is the jump pack is not wasting precious starting current/capacity charging your dead battery first, reaching voltage equilibrium, before you hit the key. Believe it or not removing the dead battery from the equation can actually make it easier on the jump pack so don't be fooled by that sort of bovine dung....
Peukert exists, even for Lithium.. For a diesel with glow plugs, and a large dead battery, they
may or
may not start the motor. If the battery is below about 10V good luck especially if you also need glow...
Unfortunately the snake oil did not work, for what I needed a jump pack to do. I have gone back to my AGM jump packs which are 22 Ah not 2.1Ah.... If I start seeing 20+Ah lithium jump packs, from legitimate companies, not some Chinese scammer, I will jump back in but 2.1Ah, sorry, not for me......