Battery Isolator - Parasitic Current

OP here. Purchased this $30 battery isolator on Amazon and installed it as part of our Renogy 40a dc2dc charger install. This BI appears to be the same unit that Keyline sells for $85.

This BI works great. Powers on the dc2dc charger when the alternator is active (>13.3v) and powers it off when it's not (<12.8v). According to the spec sheet, parasitic current is 10ma when the secondary batteries are off-line (relay open), 250ma on-line (relay closed). The resolution on my Amprobe clamp ammeter is a little sketchy at ma levels, but near as I can tell it's definitely under 20ma with the relay open. Also, this BI is only rated for "50a-70a continuous". They claim it has a 140a rating without acknowledging it's a "peak" rating---a bit misleading.

otrfun wrote:
This isolator (and many rebranded versions of it) appear to be very popular on Amazon.

I decided to place an order. I would have preferred another Trik-L-Start but they won't ship to Canada.

So I'll move the TLS to power the generator battery, and use the above isolator to charge the chassis battery. I'll add a switch on the positive I think, so that the DC to DC charger won't back feed the chassis jar.

otrfun wrote:
Got a reply back from the seller of the $85 KeyLine Battery Isolator about its parasitic current. Their reply: "Yes, it is always monitoring and takes .02 Amps to do so." 20ma is more than acceptable for our application.

FWIW, there's a number of battery isolators on Amazon that look eerily similar to the KeyLine, have the same dimensions (2.6 x 2.6 x 2), voltage cut out/in (12.8v/13.3v) and amperage specs (140a) as the KeyLine, but cost significantly less (one was only $27).

add a toggle switch on the ground and you will get it down to 0. Be aware you won't get emergency start from this,

Got a reply back from the seller of the $85 KeyLine Battery Isolator about its parasitic current. Their reply: "Yes, it is always monitoring and takes .02 Amps to do so." 20ma is more than acceptable for our application.

FWIW, there's a number of battery isolators on Amazon that look eerily similar to the KeyLine, have the same dimensions (2.6 x 2.6 x 2), voltage cut out/in (12.8v/13.3v) and amperage specs (140a) as the KeyLine, but cost significantly less (one was only $27).

There are several ways to float charge the engine battery. I use what is easiest for my set-up.

For the C, I even made a 12v plug wire thing with a plug at each end (polarity is tricky there as they reverse where joined) and can plug one into the TV 12v socket on house and the other into the dash socket on engine. That floats the engine batt from the house batt. Meant for when parked off-grid on solar for a long time so the engine batt would need a float.

BFL13 wrote:
Our truck now sits a while between TC trips so I use a small charger clamped to the truck battery and plugged into the stick-house. The "2a" charger sits at 13.4v forever; it is not like a trickle charger that shuts off.

I can't float the house batts in the TC on the truck and float the truck battery from there anymore via 7-pin like before (Chev has no isolator like a Ford does) now that I have the Renogy DC-DC in the camper, which does isolate the truck from the TC.

The Ford Class C engine batt is floated the same way with a small charger on it while the house is on converter float.

Some have a little solar set they use on the engine batt for that job.

Why not use the load terminals on the solar controllers that you have for chassis battery charging/maintenance?

otrfun wrote:

wa8yxm wrote:
There are two basic types of battery isolators and on one of them two control systems
Diode isolators have no control system bit it is possible they may present a tiny "leakage" current.. I doubt you'd be able to measure it it's that small.

Relay isolators when isolated it's 100 percent no leakage but the control system may have a voltage sensor that "draws again a very tiny amount a very very tiny amount.

In your estimation how much current translates to "tiny" leakage? Less than 50ma?

I expect less than 5 ma, and mostly zero with solenoid ignition controlled units.

I do use a Trik-L-Start for other parasitic loads on the RV chassis battery.

Our truck now sits a while between TC trips so I use a small charger clamped to the truck battery and plugged into the stick-house. The "2a" charger sits at 13.4v forever; it is not like a trickle charger that shuts off.

I can't float the house batts in the TC on the truck and float the truck battery from there anymore via 7-pin like before (Chev has no isolator like a Ford does) now that I have the Renogy DC-DC in the camper, which does isolate the truck from the TC.

The Ford Class C engine batt is floated the same way with a small charger on it while the house is on converter float.

Some have a little solar set they use on the engine batt for that job.

BFL13 wrote:

otrfun wrote:

MEXICOWANDERER wrote:
ISOLATOR covers a large territory. Which type do you have??

Haven’t purchased one yet. This isolator (and many rebranded versions of it) appear to be very popular on Amazon.

Looks like that thing is not really an isolator and it could allow some draw from the starting battery, but if the starting battery voltage falls below 12.8 it does get isolated? Not clear. I don't really understand what that thing is good for, but more coffee might help.

That's my concern. Right now we only get about 4-5 weeks before the battery voltage on our '16 Ram Cummins drops down to 12.2v (truck is not a daily driver). Even 50-100ma of parasitic from a battery isolator could potentially drop our max time between engine starts to 2-3 weeks.

wa8yxm wrote:
There are two basic types of battery isolators and on one of them two control systems
Diode isolators have no control system bit it is possible they may present a tiny "leakage" current.. I doubt you'd be able to measure it it's that small.

Relay isolators when isolated it's 100 percent no leakage but the control system may have a voltage sensor that "draws again a very tiny amount a very very tiny amount.

In your estimation how much current translates to "tiny" leakage? Less than 50ma?