此類充電器構造簡單：一般由電源變壓器和四個二極管構成的橋式整流電路組成。充電的整個過程電壓保持不變，當電池的內阻隨著充電過程越來越小，因此充電電流也越來越大，產生的熱量也越來越多。電池快充飽時發熱量最大。加速電解質的分解，從而縮短了電池的壽命。早期的廠家生產的充電器采(cai)取“小心駛得萬年(nian)船”的策略(lve)，用小電(dian)(dian)流充電(dian)(dian)，一(yi)般(ban)不(bu)超(chao)過100mA ，這(zhe)樣電(dian)(dian)池(chi)充到(dao)最后(hou)，發熱不(bu)至(zhi)于(yu)太大(da)，從而延長(chang)電(dian)(dian)池(chi)壽(shou)命。缺點是充電(dian)(dian)時間長(chang)。現在生產(chan)這(zhe)類的廠家，采(cai)用中電(dian)(dian)流充電(dian)(dian)，100～200mA 充電(dian)(dian)時間大(da)大(da)縮短(duan)，但是以犧(xi)牲電(dian)(dian)池(chi)壽(shou)命為(wei)代(dai)價。傻瓜型充電(dian)(dian)器只(zhi)能用時間來控制充電(dian)(dian)，它只(zhi)適合于(yu)深充深放的五號(hao)、七(qi)號(hao)鎳鎘、鎳氫(qing)電(dian)(dian)池(chi)。

    充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)時間：T = 1.5C/I（ C是(shi)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)容量，I是(shi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流）例：如(ru)果有個1000mAh 的(de)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)放在(zai)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流是(shi)50mA的(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)上充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)，充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)時間就是(shi)30小時。辨認(ren)這(zhe)(zhe)類充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)的(de)方法(fa)：當插上電(dian)(dian)(dian)(dian)(dian)(dian)源插頭(tou)后，充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)指(zhi)示燈一直亮(liang)著(zhu)。街上賣(mai)的(de)10～40元以(yi)內的(de)均是(shi)這(zhe)(zhe)種充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)。