Evaluate old system

Every refit begins with an inventory. It answers three questions for each component: Is it technically sound? Does it fit the future system? Will it remain accessible? One "no" is enough for the part to be placed on the replacement list — even if it is functional.

Why three questions and not one

"Still working" is the worst criterion for a refit. A fuse holder may be perfectly fine but still need to be removed because it's too small for the new distribution system or because it's located behind a panel that you no longer want to open in the future.

Conversely, not everything old is bad. Solid busbars, good main switches, and generously sized cables last for decades and are often better than their reputation. The inventory separates the two — with an eye on the planned system, not the existing one.

The walkthrough: what to look for

Tinned stranded ends in screw terminals are a common old finding: the tin flows under pressure, and the terminal loosens over time. Wire ferrules or ring terminals are the correct termination.

What only becomes visible under load

The visual inspection finds what is obvious. The rest is only found through measurement. A short load test is therefore part of the assessment: switch on a large consumer and compare the voltage at the battery bank and at the consumer.

If the difference is significantly more than three percent of the nominal voltage — i.e., more than approximately 0.36 volts in a 12-volt system — there is a problem in the circuit. The exact location is clarified by sectional measurement; for the inventory, simply determining that the circuit is not in order is sufficient.

NoteTen minutes after switching on, touch all terminal points. A noticeably warmer spot is a hit — and a fire hazard, regardless of the refit.

Assessing the battery bank

For the batteries themselves, four pieces of information are important: age, technology, condition, and installation situation. The age is usually indicated as a date code on the housing. Lead-acid batteries beyond five to six years usually go along with the replacement, even if they still perform somewhat — they will become the weak link of the new system.

The condition can only be roughly assessed without measuring equipment. A discharge test with a known load over a known time is informative; if you have a shunt, you can read it directly. Without balancing, it remains a matter of indications: How quickly does the voltage drop under load, how quickly does it recover, does the battery bank even reach the charge termination voltage anymore?

The installation situation is often overlooked but is crucial: Are the batteries secured against slipping, are the terminals protected against contact and falling tools, is the compartment ventilated? If you're rebuilding anyway, now is the time to address this.

The AC side

WarningThe assessment of the AC system is not a visual inspection. Protective earth, residual current protection, separation from shore power, and insulation resistance must be checked — with suitable equipment and by someone qualified to do so.

What can be determined without measurement is at least the question of presence: Is there a residual current device? Is the shore power inlet in order? Are AC and DC lines routed separately or are they in the same conduit? If any of these are missing, they belong on the list — regardless of how long it worked well without them.

From list to decision

The result is a table with one row per component and one of three decisions: stays, will be overhauled, will be replaced. Each "stays" includes a brief justification — it forces an honest answer to the third question about accessibility.

This list is the entry point for planning. It shows what needs to be purchased, how much work is involved, and where the stages can be meaningfully divided.

Document before the first dismantling

As soon as the first cable is disconnected, the old system can no longer be reconstructed. A series of photos — every terminal strip, every busbar, every cable run, every label — takes half an hour and will be the only available reference throughout the entire conversion.

It is usefully supplemented by labeled adhesive tapes on each wire before it is disconnected. What belongs together is rarely obvious when reassembling.

Typical mistakes

• Decided based on "still working." Fit and accessibility are equally important criteria.
• Only visually inspected. Contact resistances only become apparent under load.
• Skipped the negative side. This is the most common weak point in old systems.
• Kept old batteries. They will become the weak link in the new system.
• Included the AC side like DC. This requires tests that demand expertise.
• Did not photograph. After the first dismantling, the information is gone.

For unclear findings, a second opinion is worthwhile before ordering parts — our team will look at photos and measured values in a consultation or via the contact form.