A
start battery should ALSO be able to act as a
reserve battery... This means it should be able to both start the engine and run critical house loads in an emergency. House banks can and do suddenly fail and a small LiPo is not going to cut it when or if it does. These little batteries, usually 10Ah or less, provide cranking capability but no real ability to use them as an emergency bank other than for starting.
This failure happened to one of our members only a few months ago.
Ideally you want the ability to:
Isolate the bad bank
Switch to the healthy reserve bank in order to run the vessel
This is another reason why I use deep cycle batteries for sailboat AUX start batteries. I had one customer sail halfway to Bermuda, hand steering and with minimal electronics, when his house bank suffered an internal short. He was pretty glad he'd kept that Group 31 as his "start / reserve" bank and it did exactly what it was designed and intended to do....
I have posted this before on Li-Ion jump packs but here it is again.
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 HOWEVER we still need to consider real MATH and PEUKERT....
These little jump packs are
entertaining for the size, and the price they have come down to, but...
I bought a Noco GB-30 and it failed to start the first three 3 boats I needed it on so I returned it. I then bought the Noco GB-40 (bigger & stronger yeah right) it too failed to start boats with dead batteries.
The "capacity" of the battery in the Noco Boost was 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's of total capacity. This is actually 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 I will 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.
I also found the soldering inside the Noco to be of horrific quality and the relay that passes all the current is rated at 70A for a unit that claims 1000A.... 1000A through a 70A relay, hmmmmm??
A friend who is also an electrician bought a no-name Chinese jump pack and on the first jump one of the cables got so hot that it unsoldered itself.
Be very wary of how the mAh rating (1000mAh is 1 Ah) is derived:
For example is it a 60C, 30C, 10C, 2C or 0.2C discharge rate to earn that mAh rating? These batteries will often asked to supply a 30C plus load and on diesels often in excess of 40C. Just this morning (Sunday 7/31/16) I was trouble shooting a no start situation on a big Westerbeke diesel on a Fisher Motor Sailor. The
in-rush cranking current was 614A and the
averaged cranking current (Midtronics EXP-1000HD and Fluke 376) was still over 300A and this was after 50A of glow plug for 10-15 seconds. This is the exact type of scenario my GB-40 could not handle. Even to a massive 12,000 mAh jump pack battery or 12Ah (my Noco GB-40 was only 2.15 Ah's) delivering 614A to get a starter cranking is a 51C load or 51 X the batteries Ah capacity.
Ask the manufacturer what the Peukert of these jump packs at51 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......
