Replace battery, battery maintainer, add external volt meter

Jeep, sets outside, covered and on battery maintainer. Noted green light on 15 year old maintainer changing to red every few hours. Couple of days later finally checked batteries. Start was at 10.4, winch was at 11.2. Put both on charger. Start battery no water & dumped a cell, winch battery looks like it's ok.

Near as I can tell the maintainer dumped. Constant charge till it boiled out water, but now has no output. Batteries are tied together thru isolator but maintainer can only feed one battery. Could be the start battery dumped a cell, winch battery would feed start battery until it also drawn down and maintainer would kick in. Once it thought charged, go to trickle and cycle start all over. Problem is the no water, makes it seem like maintainer was issue. Regardless I need a new battery and charger

For maintainer I'm using what I installed in our truck. A Schumacher SC1300 1.5 Amp 6V/12V Fully Automatic Direct-Mount Onboard. https://www.amazon.com/gp/product/B07894CFCR

Old maintainer plugged into lead from battery and sat under jeep on spring. So charge status pilot could be seen. This one I'm mounting in the engine bay. Jeep is covered so need a means to see status without uncovering.

So I'm also adding an external volt meter that will read either battery.

1st the maintainer.

Relay I used, https://www.amazon.com/gp/product/B0748F1JK4/ 5 pin SPDT because I am using relay to turn OFF maintainer when trigger wire energized. (Relay must have an 87 and 87a pin, normally open and normally closed, NOT 2 87 pins).
As maintainer turns itself off when it detects no battery on its output line, simply routing its output wire thru the relay. So Jeep ignition or ACC hot sends power to relay which disconnects the output wire to battery (87a). Maintainer turns itself off-simple.

Relay. Open maintainer case, cut slot to insert metal leg of relay, remove mount leg from relay. Bend end at 90° and insert thru case, Snap relay back on leg.

To the maintainer de soldered its red out put wire and connected to the 87a normally closed terminal of relay. On the relay plug, I removed its blue and yellow wire & terminals. Inserted the yellow wire back into #30 pin position. The blue wire and terminal went into the parts box leaving terminal #87 unwired. The yellow wire, now from #30, I soldered to the output of maintainer (was the red wire).

Grounding relay #85 with screw mounting maintainer in engine bay. Trigger wire I ran from aux fuse block under dash that's hot with key in ACC or start/run for uninterrupted power. Connected to #86 of relay.
(UPDATE diagram above- wire marked to 'Battery' now goes to 3way switch on front of jeep that selects which battery is connected to charger- described at bottom of page)

Pretty simply except for running wire from dash

Not shown but cut hole for on/off switch and ran AC line/black wire thru it to manually turn off maintainer.

And mounted. AC for now is 12' extension cord routed to front of jeep. Eventually hard mount an AC female receptacle so extension cord from house just plugs in.(done!-see bottom of page) For now about 7' of cord reaches outside weather proof receptacle. Still a LOT simpler. Where before I'd unplug maintainer from jeep and outdoor receptacle, unbungee maintainer from its precarious location on top of leaf spring-carry over to shop to store. Now its just unplug ext cord roll up and store behind winch. Pretty stoked

The auto disconnect feature works- no interaction between the 2 charge sources. Though most on board maintainers ok to leave connected to battery, not meant to have energized and charging while engine starting/running.

2nd: Visual checking status of batteries

Ordered a panel mount volt meter, mostly for size of numbers, just over 5/8". Case 2 1/4x1 1/8 x 3/8 thick, perfect to mount on flat front bumper using double side tape. Only need small 3/16s hole thru for wires.

Advertized as waterproof for motorcycles. Well the wires are potted where they enter meter but the halves of case are not sealed. I opened a ran a bead of sealant (B-7000) between and resembled. But the function of this style nice. Low voltage @ 11.5 numbers flash, also at high voltage though not until like19+V so not really useful. Mute as I'm not powering constantly.

Drilled 3/16" hole thru bumper, under winch roller fairlead. Mounted meter with 3M molding tape (after wiping off text with acetone :). Drilled another hole beside it for a weather proof 3- way on/off/on DPDT switch. (could have use SPDT switch but I had this), Ran the meter wire over. From each battery I ran 2wires terminating in 2 pin SAE plugs. This is so I can check with multimeter if new meter fails or direct battery voltage for what ever reason. To these I tapped and added short branch wires to run to switch.

Connected grounds and positive leads to switch. Connect positive from meter to center of one pole, connect the ground from meter to other pole center. Connected battery positive from each battery to end poles of one side of switch. connected the grounds to other side. This switches both the ground and positive from batteries to meter. Tested, center off meter blank, flick to left reads winch battery, flick to right reads starting battery. Cool. Buried back of switch in hot glue to weather proof connections. Install switch into bumper.
ToDo : Wiring is pretty secure and isolated against chaffing etc. and unconcerned with shorting. However because they are directly connected to batteries they should be fused.

Well this was to show battery connections but it really doesn't.

From each battery pole are the wires that run to meter/switch, they have soldered ring terminals and are bolted. These positive leads are where inline fuses will be added. Or possibly add another fuse block, which thinking about it would be better.
The maintainer leads were also bolted ring terminals however I removed the positive lead ring and replaced with an alligator clamp to swap which battery is being charged without unbolting. Typically this is always connected to the start battery. If I note winch battery getting low, switch to the winch battery for a few days to ensure its topped off.

UPDATE: Rewire
Seriously thinking of adding switch to charger output. Issue is I can't interconnect batteries externally to charge, they are different. To swap which battery is connected I need to untie/uncover jeep-a pain when in storage. Take 10 minutes to add right at maintainer. Simple 3 way to select which battery receives charge instead of moving alligator clip. But what I want if I could, do without uncovering and opening hood of jeep....

Could just run new wire from charger, tie new switch output to meter switch leads...

Quandary short of rewiring (which I should)..I have 4 wires, remove ground wires at bumper meter switch, use 1 to ground meter, there common anyway. Remove other wire at battery ground, reroute to maintainer output. At bumper connect the now charger hot feed cut ground wire to feed another switch on bumper. Tap existing meter battery leads for switch outputs. Wires already there. Would be really convenient, walk up to jeep- flick meter switch to check batteries- if one low, flick another switch so that battery charges..yup. Where does this stuff come from?

Well 3 hours later final wiring. Ended up reconfiguring existing wires. Probably took 30 minuets. But...Reconnect power, turn on charger, neither battery receiving charge, its LED wouldn't go off, even when AC pulled? Back traced to discover the ground wire I repurposed had an old crimp on tap that connection failed. Weird...Not enough connection to pass charger voltage but enough charger thought battery connected and power its LED. Cut out and soldered connection-

The repurposed wire for charger feed I added fuse to make connection to charger output wire. No more switching alligator clip. Still to do is add fuses on the battery leads. Round to it...

Alls well that ends well. Works slick, can turn charger to which ever battery I wanted connected, or turn charger off, Check voltage either battery. I set both switches so to the left is winch battery, to the right is start battery, they have no effect on each other. All while the jeep is covered and tied down.
Starting jeep in storage, charger still plugged in, relay auto disconnects from battery with key on. Can turn off AC input to charger from inside engine bay without unplugging. Driving just unplug AC cord, Key on same, relay disconnects charger from batteries.

Oh last round to it, to protect the switches a bit, though due to winch roller fairlead plate unlikely to hit, making a guard. Probably just bend ends @ 90° to a short piece of flat bar. Bolted to underside of winch plate, the bent ends will hang down vertically on either side of switches.

Anyway selectable which battery to be charged, meter to read either battery..

Update

Added female AC port to back side of left front wheel well. Protected from the elements it can be left plugged It has 16" pigtail running up to charger that charger plugs into. Extension cord from power pole plugs in when needed. No more winding cord up, draped/stored on the jeep.